Low-temperature Co-fired Ceramic Technology Research Articles

Degradation-controlling mechanisms in natural organic acid solutions of CaO–Al2O3–SiO2–B2O3 glass-ceramics by partially substituting Ca2+ with Ba2+ and Sr2+

The degradation of environmentally friendly CaO–Al2O3–SiO2–B2O3 (CASB) glass-ceramics, which consist of anorthite and glass phase, was investigated in three natural organic acid solutions. The results indicated that citric acid had the most significant effect on the degradation of CASB glass-ceramics. While the chemical stability of anorthite is relatively poor, the glass phase also contributed significantly to the effective degradation of CASB glass-ceramics. Subsequently, Ba2+ or Sr2+ was used for full or partial substitution of Ca2+ in CASB glass-ceramics, and the degradation-controlling mechanism of the substituted CASB glass-ceramics was further researched. The full substitution of Ca2+ in CASB glass-ceramics by the two cations resulted in the occurrence of borate [BO4] units in the glass phases, and the interlinkage of [BO4] with broken silicate [SiO4] network structures caused a complementary network effect. Consequently, the degradation of CASB glass-ceramics by organic acids was reduced due to the improvements in the chemical stability of the modified glass-ceramics. Additionally, degradation control can also be achieved based on a mixed-alkali effect, originating from the partial substitution of Ca2+ in CASB glass-ceramics by Ba2+ or Sr2+. The degradable glass-ceramics have the potential to be applied in low-temperature co-fired ceramic technology because of their good physical properties, which include a dielectric constant of 3–5, a dielectric loss as low as 10−3, a coefficient of thermal expansion of 3–9 × 10−6/°C, and an average bending strength of about 47 MPa. Noticeably, the development of the degradable glass-ceramics is helpful to the low-cost and pollution-free recycling of valuable metal electrodes, which is significant for the sustainable development of electronic packaging technologies.

Nano cristobalite embedded Er3+ doped multi-functional silica phosphate composite glasses for optoelectronic applications

Composite silica-based glasses were synthesized with varying concentrations of Er3+ by sol-gel route. The presence of alkali sodium ions reoriented the silica tetrahedra, eventually forming the cristobalite phase in the glasses. The addition of Er3+ reduces the crystallite size from 23.8 nm to 6.9 nm, while retaining the fractional ceramic attribute for effectuating mechanical stability and ductility. Band gap energy increases with Er3+ doping by the principles of the Burstein-Moss shift, increasing transmittance to 90% in the glasses. The density of the glasses increases with erbium content, with a subsequent increase in ionic bonding as validated by the metallization criterion. Judd OFelt (JO) parameters were evaluated from the oscillator strengths of absorption transitions, identifying decreasing covalency in the glass systems. Broad bandwidth and lifetime of 79.9 nm and 6.2 ms respectively were obtained for near-infrared (NIR) transmission at 1.47 μm, suitable for an S-band telecommunication window. The material has potential red lasing performance corresponding to the transition: 4F9/2→4I15/2. Low dielectric constants and decreasing activation energy of the glass material at higher frequencies, as derived from Arrhenius plots, is suggestive of a cost-effective inter-layer dielectric substrate for microwave signal propagation. This could be favorably capitalized for micro-fabrication in integrated electronic industries, employing the Low-Temperature Co-fired Ceramic (LTCC) technology as a strategic alternative to the ceramic substrates devised otherwise using high sintering temperatures.

Broadband high‐gain low‐temperature cofired ceramic substrate integrated cavity antenna array based on high‐order mode for W‐band applications

AbstractA broadband substrate integrated cavity (SIC) antenna array based on high‐order mode is proposed for low‐temperature cofired ceramic (LTCC) integrated systems in W‐band. To improve the gain of antenna element, a large SIC is adopted to work in high‐order mode, which also avoid using excessive vias and reduce the process complexity. Two parasitic patches are loaded on the high‐order mode SIC to remove the reverse E‐field in the open aperture, leading to a high‐gain broadside radiation. The high‐order‐mode SIC antenna element is fed by high‐order TE20‐mode substrate integrated waveguide (SIW), rather than regular TE10‐mode SIW. The simplified feeding network with TE20‐mode SIW is also designed with wideband performance, further enhancing the fabrication robustness of antenna array. To validate the proposed high‐order mode‐based antenna element and feeding network, a W‐band 2 × 4 antenna array is designed as an example using LTCC technology. The measured return loss is better than 10 dB from 81.1 to 98.1 GHz (19% bandwidth) with a maximum gain of 18.3 dB at 94 GHz. The proposed antenna array has great potential in millimetre‐wave and terahertz LTCC integrated applications.

NDE-Based Failure Analysis of an LTCC-Eddy Current Sensor Exposed to High Temperature Using 3-D X-Ray μ-CT

Sensors based on Low Temperature Co-fired Ceramic (LTCC) technology have shown great potential for in-situ Structural Health Monitoring (SHM) of engineering components exposed to high temperatures (HT) [1]. LTCC is a unique of its kind materials technology offering significant advantages for the development of micro-systems with integrated sensors. Nevertheless, there are still metrological issues like thermal and mechanical stresses associated with the fabrication process and subsequently the sensor fails while in use. This communication deals with the Non Destructive Evaluation (NDE) based failure analysis of an LTCC-based Eddy Current (EC) sensor exposed to HT. It aims at monitoring the in-situ performance and efficacy of the sensor exposed to HT for prolonged duration. The sensor was instrumented and placed inside the furnace (~ 650 °C) and in-situ EC response was monitored using an automated EC measurement set-up. We found that the sensor failed to operate by losing its electrical attributes after ~ 350 hours of continuous operation. Subsequently, a detailed investigation on NDE-based failure analysis of the sensor was carried out using an ultra-high resolution 3D X-ray μ-Computer Tomography (μ-CT) imaging system. The most common flaws include alignment errors, conductor swelling, conductor creeps, layer shrinkage, interconnect via voids, coil expansion and micro-cracks on conductor tracks and pads. A comparison study is drawn to create a database that will lead to optimizing the fabrication process flow and setting operational limits of the LTCC sensor.

Synergetic modulations in Ag2CaV4O12 via cation substitution and composite formation to optimize dielectric performances

Low-temperature co-fired ceramics technology (LTCC), as a remarkable integrated technology developed in recent years, has become the mainstream implementation of passive integration. Ceramic materials as the dielectric layers are required to have low sintering temperatures (<900 °C) to facilitate co-firing with conductive materials such as Ag and Cu. Herein, a series of low-firing dielectrics Ag2-xNaxCaV4O12 (x = 0.1, 0.2, 0.3, and 0.4) were designed for potential application in LTCC. Such ceramics can be densified at extremely low temperatures (500–540 °C) with high relative densities (>95%), and possess promising dielectric properties (εr = 7.3 ∼ 7.5, Q×f = 48,500 ∼ 59,800 GHz, and τf = −55.3 ∼ −29.4 ppm/°C). CaTiO3 was added as a τf compensator to tune the thermal drift of resonance frequency, yielding a near-zero τf value combined with an εr = 8.6 and Q×f = 47,100 GHz. Chemical compatibility with silver was also evaluated, rendering their application possible in LTCC.

Wideband and low‐loss transition from low‐temperature co‐fired ceramic laminated waveguide to subminiature coaxial connector for millimetre‐wave applications

This letter presents a novel transition scheme from laminated waveguide (LWG) to subminiature coaxial connector with wideband and low-loss performance. The laminated waveguide is achieved using multilayer low-temperature co-fired ceramic (LTCC) technology. In the conventional transition scheme, a length of grounded coplanar waveguide (GCPW) is used to connect the LWG and coaxial connector to obtain a wide bandwidth, which increase the transition size and radiation loss, especially in millimetre-wave (MMW) band. To realize a compact and low-loss LWG-to-coaxial connector transition, the GCPW line is removed and the whole LTCC transition structure is designed underneath the coaxial connector. Moreover, two stages of waveguide step are introduced to constrain the electromagnetic field in the transition for lower radiation loss, which also contributes to the wideband impedance matching. The back-to-back transition is designed and fabricated with LTCC technology to validate the proposed transition scheme. A measured bandwidth of 44% from 27.3 to 42.9 GHz is achieved under |S11| < −15 dB and the insertion loss of single transition is about 0.4 dB.

In-Line Vector Modulator Integration in Dielectric-Filled Waveguide

This paper proposes a scalable substrate-integrated waveguide (SIW) module accommodating an in-line vector modulator monolithic millimeter integrated circuit (MMIC). The SIW module is realized with low-temperature co-fired ceramic (LTCC) technology, and it can be inserted in a dielectric-filled waveguide (DFWG). The module combines λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i></sub> /4-transformer-based E-plane tapering and SIWs on LTCC with the wire-bonded vector modulator. The proposed active LTCC module and two passive test structures (i.e., a constant-height-SIW module and a SIW module with E-plane taperings) are manufactured and tested as in-line modules in a DFWG. The passive test structures with the waveguide-to-DFWG and DFWG-to-SIW transitions measure 3.1 dB and 4.6 dB of insertion loss on average, respectively, at the 71–81 GHz frequency range. The active LTCC module measurements demonstrate a dielectric-filled waveguide with phase and amplitude tuning capability and gain up to 17.6 dB within the same frequency range. A four-channel mock-up module with λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /2 channel spacing is designed and manufactured to demonstrate the scalability of the design.

Novel ultra-low loss and low-fired Li8MgxTi3O9+xF2 microwave dielectric ceramics for resonator antenna applications

Low temperature sintered Li8MgxTi3O9+xF2 microwave dielectric ceramics with x = 2−7 were developed based on a newly designed pseudo ternary phase diagram of the Li2TiO3–MgO–LiF system. Dense solid solution ceramics (of relative density >96 %) with cubic rock-salt structure, accompanied by a small amount of secondary phase MgO, were obtained in the temperature range of 800−925 °C. With increasing Mg2+ content, the value of εr decreased, whereas that of τf remained nearly constant, and the Q×f increased to a maximum at x = 5. The Li8Mg5Ti3O14F2 ceramic sintered at 875 °C exhibited superior microwave dielectric properties with εr= 16.8, Q× f= 119,700 GHz, and τf= −41.6 ppm/°C. The good compatibility with Ag electrodes highlights the promising prospects of this ceramic in low-temperature co-fired ceramic technology. Furthermore, a dielectric resonator antenna fabricated based on a Li8Mg5Ti3O14F2 ceramic exhibited an outstanding S11 of −34.7 dB and a broad bandwidth of 360 MHz at the desired resonant frequency of 5.98 GHz.

High sensitivity and selectivity microwave biosensor using biofunctionalized differential resonant array implemented in LTCC for Escherichia coli detection

A novel method for label-free detection of Escherichia coli relying on microwave sensing is proposed. A transmission-type differential resonator array biosensor covered with polyclonal anti-Escherichia coli antibodies is introduced providing a robust response with high sensitivity for detecting bacteria presence due to resonant operation combined. The high selectivity is given by the presence of specific bacteria-binding antibodies. Low-Temperature Co-Fired Ceramics technology is proposed to be used for implementation to take advantage of its quasi-three-dimensional fabrication capability. The proposed sensing structure operates in a frequency range of 4 – 6 GHz with five distinct resonances increasing the probability of bacteria detection presence. The developed sensor was experimentally validated by measurements of various concentrations of Escherichia coli along with measurement of a non-specific high concentration of Lactobacillus rhamnosus LOCK 0919. The obtained results prove the performance and suitability of the proposed biosensor for biomedical applications.

Novel copper borate ceramics with lithium-based sintering aids for LTCC terahertz applications

Novel CuB2O4–Cu3B2O6 substrates doped with three Li-based sintering aids, Li2WO4, LiBO2 and Li2CO3, were prepared using the LTCC (low temperature cofired ceramic) technology.

Method of Designing a Planar Scan Angle Enhancing Metalens Featuring Lossless Wide Scanning at mmWave

For the first time, a method to design a planar scan angle enhancing lens with minimum beam distortion for automotive radar at millimeter-wave is presented. The proposed lens is not only advantageous regarding its planar topology but also offers a solution to the chronic problem surrounding planar phased array antenna and planar lenses: scan loss. In this article, ray optics and ray transfer matrix are applied to Galilean lens configuration from which the concept of scan enhancement and compensating parameters are conceived. The basic idea of compensating lies in re-focusing the portion of the beams and suppressing transmission at extreme angles. Visual analysis of the wave refraction and designing of the lens system is conducted using 2-D ray-tracing code. Full-wave simulation validates the effectiveness of the proposed idea by extending the limited scan range of the phased array antenna from 45° to 58° with gain fluctuation below 1.1 dB at E-band. The radiation efficiency is calculated to be 0.86 at 76.5 GHz. Furthermore, the proposed lens system is fabricated using low-temperature co-fired ceramic (LTCC) technology and experimentally verified. Series-fed array antennas integrated with scan angle enhancing meta lens (SAEMLs) confirmed the shift of the gain peak from 46° to 58°, proving that SAEML can effectively extend the scanning range of phased arrays with small gain variation.

A Novel Wideband Transition from LTCC Laminated Waveguide to Air-Filled Rectangular Waveguide for W-band Applications.

In this paper, a novel wideband transition from a laminated waveguide (LWG) to an air-filled rectangular waveguide (RWG) is proposed for millimeter-wave integration solutions based on multilayer low-temperature co-fired ceramic (LTCC) technology. The integrated transition cavity is divided into several resonators by introducing five grounded via holes. Due to the magnetic wall existing in the symmetry plane, the equivalent circuit of the proposed transition can be simplified as a three-pole filter model to explain the working mechanism with wideband performance. A W-band integrated LWG-to-RWG transition is designed as an example using LTCC technology. Two back-to-back prototypes with different lengths are fabricated and measured. A measured 25.7% bandwidth from 76 GHz to 101 GHz can be achieved for return loss better than 14 dB. The average insertion loss of a single transition is about 0.5 dB. The compact structure and wideband performance give it potential in high-density millimeter-wave and terahertz packaging.

Low temperature co-fired ceramic (LTCC)- based biosensor for detection of vanadium using immobilized Arachis hypogaea alkaline phosphatase on multi walled carbon nanotubes ethyl cellulose sponge matrix

Studies on enzyme based thermometric biosensor are limited. Here, we report on fabrication of an alkaline phosphate based thermometric biosensor. We designed alkaline phosphatase inhibition based biosensor for detection of vanadium using immobilized alkaline phosphatase on multi walled carbon nano tubes (MWCTs) ethyl cellulose sponge matrix. We isolated protein from plant source, partially purified and fabricated a miniature ceramic viz. LTCC (low temperature co-fired ceramics technology) based biosensor for detection of vanadium. This biosensor consists of a microreaction chamber with buried heaters. Alkaline phosphatase has been isolated from the seeds of ‘Arachis hypoghaea’ was studied for its biochemical properties viz. optimum pH and temperature. The partially purified enzyme was immobilized using carboxyl-functionalised carbon nanotubes (CNTs) by cross linking with epichlorohydrin (ECH) along with a matrix of ethyl cellulose. The developed LTCC based biosensor on testing indicated its linear response to vanadium concentration up to 9 mM with a relatively high sensitivity of about 147 nA/mM. Thus, we have demonstrated a LTCC based biosensor using immobilized alkaline phosphatase for detection of vanadium.

The application of Low-Temperature Cofired Ceramics technology in Gas Electron Multiplier microstructures

The main goal of the work is to develop a novel technique for the production of improved Gas Electron Multiplier (GEM) microstructures that are critical elements of particle detectors used for High Energy Physics research. Invented at CERN, the Micro-Chemical-Vias (MCV) technology has proven optimal for producing high volumes of large size GEMs elements. We aim to develop a technology for the production of GEMs with higher vias densities, increasing the gain of a single structure and ensuring better system reliability. Additionally, different conductive layers are planned for use. Tests were carried out using Low-Temperature Cofired Ceramics (LTCC) and various types of conductive layers.

Software development methodology of structural-parametric description of low-temperature co-fired ceramics-technology for the production of microwave components

The article discusses the production of microwave components based on the technology of low-temperature co-fired ceramics (LTCC). A set of standards Continuous Acquisition and Life cycle Support (CALS) and International Organization for Standardization (ISO) and business process models in these standards are considered. Based on the basic models of the ISO and CALS standards, a structural-parametric description model (SPD) has been developed, in which the structure of ISO-9000 is preserved, and specific parameters of LTCC technology are added. The methodology of the (SPD) of this technology is proposed. Open source software for processes, resources, results, production operations, control and management has been developed for each technological operation (TO), workplace and area. The methodology for creating information support and Microsoft Access Database Management System (DBMS) of SPD is proposed. Recommendations for the development of a software-methodological complex of information support for SPD of LTCC technology are proposed.

Flow-based green ceramics microdevice with smartphone image colorimetric detection for free chlorine determination in drinking water

The residual free chlorine concentration is an important parameter to evaluate the potability of water and the efficiency of disinfection in the water treatment system. As a restricted range of residual free chlorine concentration at all points of the distribution network is needed to ensure efficiency and to avoid deleterious effects, fast and in situ quantification of this specie is important. This work deals with the development and validation of two procedures based on DPD (N,N-diethyl-p-phenylenediamine) and OT (ortho-tolidine, 3,3-dimethylbenzidine) for the determination of residual free chlorine in water by exploiting a flow-based microdevice built with Low Temperature Co-Fired Ceramic (LTCC) technology. The analytical signal was monitored by a smartphone camera through RGB values obtained by a free application (Color Grab®). Under optimized conditions, linear ranges within 0.6–2.5 mg/L and 0.1–2.3 mg/L were obtained for DPD and OT methods, with limits of detection and quantification of 0.023 and 0.077 mg/L (DPD) and 0.026 and 0.089 mg/L (OT). Precision expressed as RSD (2.0 mg/L free chlorine, n = 10), was 1.3 % and 0.7 %, respectively. Both procedures were successfully applied to the analysis of samples from a water treatment plant. The flow-based microdevice coupled to digital-image colorimetry is an innovative, sustainable, and cost-effective analytical tool for in-field chemical analysis.

Low‐temperature‐sintered MgO‐based microwave dielectric ceramics with ultralow loss and high thermal conductivity

AbstractWith the development of 5G/6G communication, the requirements of portable devices for miniaturization and multifunction make low‐temperature co‐fired ceramic (LTCC) more and more important. In the area of high‐frequency high‐density passive integration, microwave dielectric ceramics with a low dielectric loss and high thermal conductivity are urgently needed to ensure the effective signals transmission and system reliability. However, most microwave dielectric ceramics with a low dielectric loss were not applicable for the LTCC technology due to the high sintering temperature. In this work, a series of MgO‐based ceramics [(100 − x) wt.% MgO–x wt.% (0.2SrF2–0.8LiF) (x = 5,7,10)] were prepared by solid‐state reaction method. The addition of sintering aid 0.2SrF2–0.8LiF (S2L8) decreased the sintering temperature below 880°C without degrading the microwave dielectric properties of ceramics. Microwave dielectric properties of ceramics, including quality factor Q × f, relative permittivity εr, and temperature coefficient of resonant frequency τf, were investigated to find the optimum composition and sintering temperature. In general, MgO–7 wt.% S2L8 ceramic sintered at 860°C exhibits outstanding properties of Q × f = 180 233 GHz, εr = 9.11, τf = −40.33 ppm/°C, and a high thermal conductivity of 24.02 W/(m K). This series of ceramics are suitable to be co‐fired with Ag electrodes. With all those great properties, this series of MgO‐based ceramics are expected to be the candidates for LTCC applications in 5G/6G technology.

Producing high quality LTCC sensors for ITER in-vessel magnetic diagnostics

Inductive magnetic sensors inside the vacuum vessel of ITER tokamak are crucial for plasma operation, plasma control and physics studies. This set of sensors was designed based on the LTCC (Low Temperature Co-Fired Ceramic) technology in order to survive the hostile environment inside ITER vacuum vessel with restricted space, high vacuum, high heat load, and high radiation level. Some features were also integrated into the sensor design to address specific service loads, for instance, accidental superheated steam intrusion. As per ITERs diagnostics design, in total 300 LTCC magnetic sensors have been successfully produced according to the manufacture design and following the specifically developed fabrication process. Extensive quality control program and rigorous factory acceptance tests had been implemented throughout mass production (final 300 sensors). These practices ensured that the sensors were produced to the desired quality and with high reliability.

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.