Low-temperature Co-fired Ceramic Technology Research Articles

Influence of substituting Na+ for Mg2+ on the crystal structure and microwave dielectric properties of Mg1-xNa2xWO4 ceramics

The Mg1-xNa2xWO4 (0 ≤ x ≤ 0.14) microwave dielectric ceramics were prepared through traditional solid-state reaction and sintered at 875−925 °C for 4 h. Compared with pure MgWO4 ceramic, the samples with substituting Na+ for Mg2+ could be sintered at a lower temperature, the quality factor values and the densification of microstructure were obviously improved. Raman spectroscopy proved that the relative permittivity was related to the multiple phases and molecular polarizability. In addition, the distortion of[MgO6] octahedron also changed, resulting in resonance frequency temperature coefficient varied nonlinearly from x = 0 to 0.14. Considering the applications of low temperature co-fired ceramics technology, the Mg1-xNa2xWO4 (x = 0.06) ceramic sintered at 875 °C had the best performance. Not only did it have excellent microwave dielectric properties of εr = 10.474, Q × f = 45,868 GHz, and τf = −69 ppm /ºC, but also presented great chemical compatibility with the commonly used Ag electrode.

A novel low sintering temperature scheelite-structured CaBiVMoO8 microwave dielectric ceramics

Abstract Novel medium-permittivity scheelite-structured CaBiVMoO8 ceramics were prepared by a solid-state reaction route. The effects of sintering temperature on the phase composition, microstructure and microwave dielectric properties of CaBiVMoO8 ceramics were investigated systematically. The Rietveld refinements of X-ray data revealed all samples were well crystallized in space group I41/a. All the samples exhibited a closely packed grain morphology and discernable grain boundaries. The relationship between microwave dielectric properties and bulk density of samples at different sintering temperatures was further researched. Besides, the lattice energy was one of the important factors affecting the Q×f values of CaBiVMoO8 ceramics. The temperature coefficient of resonant frequency (τf) could be slightly affected by sintering temperature. The CaBiVMoO8 ceramics were expected to be applied to low temperature co-fired ceramics technology. In this paper, the CaBiVMoO8 ceramics exhibited excellent properties sintered at 850 °C for 4h: er ∼ 40.55, Q×f ∼ 16,670 GHz, τf ∼ +55.90 ppm/°C.

Willemite with Li2CO3 as a sintering aid for LTCC microwave substrates

PurposeThe purpose of this paper is to report on fabrication procedure and present microstructure and dielectric behavior of willemite ceramic material with addition of 5% Li2CO3 as a sintering aid.Design/methodology/approachThe samples were fabricated by ball milling of the ceramic powders, preparation of granulate and pressing and co-firing using temperature profile based on heating microscope observation. The dielectric properties of the material were measured by impedance spectroscopy (Hz-MHz), transmission method (GHz) and time domain spectroscopy (THz). The composition and microstructure of the material were investigated using X-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy analysis. Ceramic powder was used to fabricate a green tape and low temperature co-fired ceramics (LTCC) multilayer structures, which in the next steps of the research were examined at the angle of cooperation with conductive pastes, strength and geometric repeatability.FindingsThe fabricated material showed low sintering temperature (920°C–960°C), low dielectric constant 6.2–6.34 and low dissipation factor at the level of 0.004–0.007. As LTCC material, willemite with 5% Li2CO3 addition showed good compatibility with AgPd conductive paste.Originality/valueSearch for new materials with low dielectric constant, applicable in LTCC technology, and development of their fabrication procedure are important tasks for the progress in modern microwave circuits.

Li2Zn3Ti4O12 Low-Temperature Co-Fired Ceramic with Li2O–B2O3–SiO2 Additive

Amaterial for low-temperature co-fired ceramic technology was developed in the Li2O–ZnO–TiO2 system for use in the manufacture of electronic components. The sintering temperature of the material was lowered from 1075 to 950°C by introducing 3% of a sintering additive with a eutectic composition in the Li2O–B2O3–SiO2 system. The developed ceramic obtained at 950°C is characterized by density 4.14 g/cm3 together with the following dielectric properties: permittivity e = 23.1 and dielectric Q factor Q f = 832 MHz.

Structure, spectral analysis and microwave dielectric properties of novel x(NaBi)0.5MoO4-(1-x)Bi2/3MoO4 (x = 0.2 ∼ 0.8) ceramics with low sintering temperatures

Herein, the x(NaBi)0.5MoO4-(1-x)Bi2/3MoO4 (xNBM-(1-x)BMO, x = 0.2 ∼ 0.8) microwave dielectric ceramics with low sintering temperatures were prepared via the traditional solid-state method to adjust the τf value and dielectric constant. The crystal structure was determined using X-Ray diffraction and Raman spectroscopy, the microstructure was investigated using scanning electron micrograph and energy disperse spectroscopy, and the dielectric properties were studied using a network analyser and infrared spectroscopy. For the xNBM-(1-x)BMO composite ceramics, the (NaBi)0.5MoO4 tetragonal phase coexisted with the Bi2/3MoO4 monoclinic phase. With the rise of x value, the permittivity increased from 23.7–29.8, and the τf value shifited from -53.3 ppm/°C to -13.7 ppm/°C. The 0.8NBM-0.2BMO ceramic sintered at 680 °C possessed excellent microwave dielectric properties with a εr = 29.8 (6.7 GHz), a Qf = 11,800 GHz, and a τf = -13.7 ppm/°C. These results made the xNBM-(1-x)BMO composite ceramics great candidates in low temperature co-fired ceramics technology.

An ultra-low-firing NaBi3V2O10 ceramic and its dielectric properties at RF and microwave frequency bands

An ultra-low-firing NaBi3V2O10 ceramic, fabricated at 620 °C by a solid-state route, was studied in terms of microstructure, dielectric properties, and chemical compatibility with aluminum electrodes for the first time. NaBi3V2O10 crystalized in a primitive triclinic structure P1 and developed a dense microstructure, and exhibited good chemical compatibility with aluminum. These merits render its potential utilization in low-temperature cofired ceramic technology. However, the microwave dielectric properties of NaBi3V2O10 are unsatisfactory with er ~ 26.0, Q × f ~ 3200 GHz, and τf ~ − 88.3 ppm/°C. Based on RF dielectric characterizations of relative permittivity and impedance over a broad frequency and temperature range, the relatively low-quality factor was explained by the oxygen vacancies caused by sintering and Na and Bi volatilization. These results imply an optimization potential in dielectric properties of NaBi3V2O10 through compositional and processing adjustments. This work also provides an alternative paradigm to evaluate the performances of microwave dielectric properties.

60 GHz Dual-Polarized High-Gain Planar Aperture Antenna Array Based on LTCC

Novel designs of planar aperture antenna (PAA) arrays are proposed in this article, which achieve dual-polarized and high-gain performances in the 60 GHz unlicensed band. In order to achieve high gain, the original PAA is expanded to its two-dimensional array form, and the two linear polarizations share the same apertures. The two polarizations are realized by using orthogonal coupling slots excited by substrate-integrated waveguide (SIW) power dividers below. Two array prototypes with $8 \times 8$ and $16 \times 16$ radiation cells are designed and manufactured based on low-temperature co-fired ceramic (LTCC) technology for ease of integration. The simulated results show that the two antennas have −10 dB impedance bandwidth and 3 dB gain bandwidth of 57.5–65 and 57–64 GHz, respectively, with stable, no-squint, and symmetrical beams in band, which is verified by measurements. Compared with other reported high-gain and dual-polarized millimeter-wave antennas, the proposed antennas feature a low-profile, simple structure while keeping high aperture efficiency. The proposed antennas are very suitable for integration and are promising in 60 GHz short-range communication applications.

Fluorescence Sensing Platforms for Epinephrine Detection Based on Low Temperature Cofired Ceramics.

A novel fluorescence-sensing pathway for epinephrine (EP) detection was investigated. The ceramic-based miniature biosensor was developed through the immobilization of an enzyme (laccase, tyrosinase) on a polymer—poly-(2,6-di([2,2′-bithiophen]-5-yl)-4-(5-hexylthiophen-2-yl)pyridine), based on low temperature cofired ceramics technology (LTCC). The detection procedure was based on the oxidation of the substrate, i.e., in the presence of the enzyme. An alternative enzyme-free system utilized the formation of a colorful complex between Fe2+ ions and epinephrine molecules. With the optimized conditions, the analytical performance illustrated high sensitivity and selectivity in a broad linear range with a detection limit of 0.14–2.10 nM. Moreover, the strategy was successfully used for an EP injection test with labeled pharmacological samples.

Review of LTCC Technology for Millimeter Waves and Photonics

VTT Technical Research Centre of Finland Ltd. has developed and utilized Low Temperature Co-fired Ceramic (LTCC) technology for about 25 years. This paper presents our activities related to photonics and millimetre-waves, including also a relevant literature survey. First a short summary of the technology is given. Especially, the unique features of LTCC technology are described in more details. In addition, several examples have been given to show the validity of LTCC technology in these high-performance fields.

LTCC Flow Sensor with RFID Interface.

The idea of battery-less flow sensors and their implementation in wireless measurement systems is presented in this research article. The authors take advantage of their latest achievements in the Low Temperature Co-fired Ceramic (LTCC) technology, RadioFrequency Identification (RFID) technique, and increasing availability of low power electronics in order to get rid of the need to use electrochemical cells in a power supply unit of the elaborated device. To reach this assumption, special care has to be put on the energy balance in such an autonomous sensor node. First of all, the new concept of an electromagnetic LTCC turbine transducer with a signal conditioner which only draws a current of around 15 µA, is proposed for measuring a flow rate of fluids. Next, the autonomy of the device is showed; measured data are gathered in a microcontroller memory and sent to a control unit via an RFID interface which enables both information exchange and power transfer. The energy harvested from the electromagnetic field is used to conduct a data transmission, but also its excess can be accumulated, so the proposed sensor operates as a semi-passive transponder. The total autonomy of the device is achieved by implementing a second harvester that continually gathers energy from the environmental electromagnetic field of common active radio systems (e.g., Global System for Mobile Communications (GSM), wireless network Wi-Fi).

A Low-profile Ultra-wideband LTCC Based Microstrip Antenna for Millimeter-wave Applications under 100 GHz

In this paper, a low profile ultra-wideband microstrip antenna is proposed for millimeter wave applications below 100 GHz to meet the demands of high data rates in the future wireless communication systems. The proposed antenna consists of a non-uniform hexagon shape radiating element on the top of 13th layer of ceramic. The proposed antenna geometry is designed using Low Temperature Co-fired Ceramic (LTCC) technology for 3D multilayer vertical integration. HFSS and CST Studio are used for design and simulation of this ultra-wideband antenna. This antenna covers a bandwidth of 33.5 GHz that ranges from 62.5 GHz to more than 96 GHz with a peak gain of 5.7 dBi, stable radiation pattern across the bandwidth, and compact size of 3.16  3.2 mm 2. The limitation of the narrow band in microstrip antenna is successfully dispensed by increasing the matching impedance bandwidth to more than 40 %. The proposed microstrip antenna is very useful for modern wireless communication systems because of its capability of covering a very wide bandwidth with favorable impedance matching and a stable radiation pattern at the considered frequency range. This antenna has another advantage in terms of the ability to be directly integrated with other RF chips using LTCC multilayer technology.

Compact Ku‐band LTCC bandpass filter using folded dual‐composite right‐ and left‐handed resonators

A compact Ku-band bandpass filter is proposed by using low-temperature cofired ceramic (LTCC) technology in this Letter. For miniaturisation, the folded dual-composite right- and left-handed (D-CRLH) resonator is introduced. By folding the inter-digital capacitor and microstrip section inductor in multiple metal layers, the circuit size of D-CRLH resonator can be reduced to one third of the planner one. Furthermore, the additional transmission loss caused by reverse currents is also investigated. To this end, a very compact LTCC filter is designed, fabricated, and measured, with the core circuit size smaller than 0.91 × 0.95 × 0.29 mm 3 . The minimum insertion loss is 1.95 dB at 13 GHz while with wide stopband suppression from 14.3 to 33.1 GHz.

Quad-Mode LTCC Surface Mounted Packaging Common-Mode Filter Based on the Asymmetric Short-Stub Loaded Resonator

A novel quad-mode common-mode filter (CMF) with ultra-wideband and high common-mode (CM) rejection-level is proposed based on the asymmetric short-stub loaded resonator (ASSLR). By utilizing the ASSLR, four resonant modes can be introduced for the initial CMF design under the even-mode operation, and correspondingly generate four CM transmission zeros. However, the initial CMF design achieves a weak CM noise suppression performance. Then, the CMF using the modified ASSLR is proposed for CM stopband enhancement. Finally, a surface mounted packaging CMF prototype is fabricated with the physical size of 6mm×4.5mm×0.6mm by using low-temperature co-fired ceramic (LTCC) technology. The measured results agree well with the simulated ones. The proposed quad-mode CMF exhibits excellent performances including high differential-mode cutoff frequency (10GHz), and an ultra-wide -15dB CM stopband with a fractional bandwidth of 104.5%.

Wideband and Miniaturized Forward-Wave Directional Coupler Using Periodical Parallel Plates and Vertical Meander Lines

A wideband and miniaturized forward-wave directional coupler using periodical loaded LC network is proposed in this brief. The loaded LC network consists of parallel plates and vertical meander lines. The coupler is designed with impedance matching, and a large phase difference with a small variation between the even and odd modes within a wide frequency range. These propagation characteristics are calculated and predicted by a unit cell using Bloch-Floquet theorem. Finally, a prototype is fabricated by low-temperature co-fired ceramic (LTCC) technology. The electric length of the proposed coupler is 1.52 ${\boldsymbol{\lambda }}$ g . The operating bandwidth of the coupling level of 1.5 dB is from 5.5 to 9 GHz, and its fractional bandwidth is 48.28%. Good agreement is achieved between the simulated and measured results.

A Ka-Band Wideband Dual-Polarized Magnetoelectric Dipole Antenna Array on LTCC

A Ka -band wideband dual-polarized magnetoelectric (ME) dipole antenna with the feeding structure consisting of two orthogonal L-shaped probes with different heights is presented based on the low-temperature cofired ceramic (LTCC) technology. A simulated overlapped impedance bandwidth of 42.5% is achieved together with an isolation of higher than 24 dB between the two input ports and stable radiation characteristics over the operating band. By combining the radiating elements with a single-layered feed network composed of microstrip lines, a $4\times 4$ dual-polarized ME dipole antenna array is designed, fabricated, and measured. An overlapped impedance bandwidth of 45% that can cover the entire Ka -band, a gain up to 16.1 dBi, and stable symmetrical radiation patterns in the two orthogonal planes with cross polarization of less than −15 dB are experimentally confirmed. With advantages of the compact geometry, wide operating band, and promising radiation performance, the proposed antenna array with dual polarization would be attractive for millimeter-wave wireless applications in Ka -band.

High-Q and near-zero τf composite Li2Mg2TiO5-Sr3(VO4)2 ceramics for low-temperature co-fired ceramic applications

In the first part of this study, the effects of LiF additives on the phase constitution, microstructure, and microwave dielectric properties (MDPs) of Li2Mg2TiO5 ceramic were studied systematically. The addition of LiF not only effectively lowered the sintering temperature but also considerably improved sinterability and quality factor simultaneously. The Li2Mg2TiO5+4 wt% LiF ceramic sintered at 900 °C for 4 h presented optimum MDPs with εr = 14.6, Q × f = 128,500 GHz and τf = -35.6 ppm/°C. Its relatively large negative τf value could be counteracted to near zero by Sr3(VO4)2 for the first time. In the second part of the study, a series of (1-x)[Li2Mg2TiO5+4 wt% LiF]-x[Sr3(VO4)2+1 wt% B2O3] (abbreviated as (1-x)[LMT+4LiF]-x[SV+1B2O3]) (0.25 ≤ x ≤ 0.4) composite ceramics were designed and prepared through the traditional solid-state sintering route. The XRD patterns revealed that Li2Mg2TiO5 and the Sr3(VO4)2 phase could be well coexisted and no impurity phase was detected. A near-zero τf value of -1.6 ppm/°C was obtained in the 0.65[LMT+4LiF]-0.35[SV+1B2O3] ceramic with εr of 13.4 and high Q×f of 91,860 GHz. The excellent chemical compatibility of the ceramic with Ag was confirmed through co-firing at 900 °C for 2 h. All results indicate that the composite 0.65[LMT+4LiF]-0.35[SV+1B2O3] ceramic can be applied to low-temperature co-fired ceramic technology.

A novel tungstate Li3Nd3W2O12 with garnet structure for low-temperature cofired ceramic technology

Microwave dielectrics sintered at low temperature are pursued for energy saving and cofiring with cost-effective metallic electrodes (e.g. Cu, Ag and Al). In this study, a novel tungstate low-firing microwave dielectric ceramic, Li3Nd3W2O12, which can realise co-firing with Ag electrode at 940 °C, was synthesised by the conventional solid-state reaction method. According to the X-ray diffraction and Rietveld refinement results, Li3Nd3W2O12 crystallised in the garnet structure with a space group of Ia3¯d and W6+ cations fully occupying the octahedral-coordinated site. The optimum microwave dielectric properties with permittivity of ∼9.8, quality factor of ∼36,800 GHz and temperature coefficient of resonant frequency of ∼ –30 ppm/°C were obtained after sintered at 940 °C. A near-zero temperature coefficient of resonant frequency of +3.6 ppm/°C was achieved in 0.96Li3Nd3W2O12-0.04CaTiO3 ceramics. These properties make tungstate Li3Nd3W2O12 a promising candidate for low-temperature co-fired ceramic technology.

Design, Simulation, and Experiment of an LTCC-Based Xenon Micro Flow Control Device for an Electric Propulsion System

A xenon micro flow control device (XMFCD) is the key component of a xenon feeding system, which controls the required micro flow xenon (µg/s–mg/s) to electric thrusters. Traditional XMFCDs usually have large volume and weight in order to achieve ultra-high fluid resistance and have a long producing cycle and high processing cost. This paper proposes a miniaturized, easy-processing, and inexpensive XMFCD, which is fabricated by low-temperature co-fired ceramic (LTCC) technology. The design of the proposed XMFCD based on complex three-dimensional (3D) microfluidic channels is described, and its fabrication process based on LTCC is illustrated. The microfluidic channels of the fabricated single (9 mm diameter and 1.4 mm thickness) and dual (9 mm diameter and 2.4 mm thickness) XMFCDs were both checked by X-ray, which proved the LTCC method’s feasibility. A mathematical model of flow characteristics is established with the help of finite element analysis, and the model is validated by the experimental results of the single and dual XMFCDs. Based on the mathematical model, the influence of the structure parameters (diameter of orifice and width of the groove) on flow characteristics is investigated, which can guide the optimized design of the proposed XMFCD.

W-Band LTCC Circularly Polarized Antenna Array With Mixed U-Type Substrate Integrated Waveguide and Ridge Gap Waveguide Feeding Networks

In this letter, a low-temperature co-fired ceramic (LTCC) substrate integrated 8 × 8 circularly polarized (CP) antenna array is proposed for the wideband and high-gain W-band antenna-in-package application. By introducing the planar L-probe together with the original coupling probe, the E-fields in the substrate-integrated-waveguide (SIW) cavity are changed, and additional E-field components with a 90° phase difference are produced. Then, a CP antenna array is obtained. To reduce the losses in the feeding network, the gap waveguide technology is utilized with the SIW technology, as a mixed feeding network. To validate the proposed CP antenna array design, an 8 × 8 CP antenna array is fabricated by the LTCC technology and measured. Measured results show that the LTCC CP antenna array obtains a gain of 22.3 dBi, and its axial-ratio (AR) bandwidth is from 89 to 98.5 GHz for AR <; 3 dB. Besides, good agreements of the radiation patterns between the simulations and measurements are achieved within the operational frequency range.

$W$ -Band High-Gain Substrate Integrated Cavity Antenna Array on LTCC

A $4\times4$ high-gain substrate integrated cavity (SIC) antenna array using multilayered low-temperature cofired ceramic (LTCC) technology is proposed and designed for $W$ -band applications. The TM211 mode of the SIC is utilized. Two parasitic patches are introduced on the top surface of the SIC to adjust the aperture electromagnetic field distribution of the TM211 mode in the cavity for obtaining a high-gain broadside radiation pattern. A bow tie shape is adopted for the parasitic patches to improve the matching characteristic of the SIC. The SIC is modified to a stepped flared shape to improve the gain characteristic of the antenna element. Subsequently, a two-layer low-loss substrate integrated waveguide (SIW) feeding network is designed for the $4\times4$ antenna array on the basis of the proposed high-gain SIC radiating element. The proposed antenna array shows a wide measured bandwidth of 17.48% from 81.45 to 97.05 GHz at $\vert \textrm {S}_{11} \vert dB and a measured gain of up to 20.3 dBi.