Multilayer Low Temperature Co-fired Ceramic Research Articles

Vertical Integration of Passive Microwave Components Using Functional Via Structures in LTCC Multilayer Substrates

A recently developed concept for designing passive microwave components using functional vertical interconnect accesses (vias) for vertical integration in printed circuit boards (PCBs) is extended and transferred to the low temperature cofired ceramic (LTCC) technology. Given the changed material properties and new technology constraints, it is shown how and to what extent the controlled vertical interconnect accesses (via) structures can behave as quasi-transmission lines, thus allowing for another degree of freedom in component design. To demonstrate the validity and utility of functional vias, several novel microwave components are proposed and subsequently analyzed including vertically integrated 2- and 3-way Wilkinson power dividers, as well as vertically integrated 90° and 180° hybrid couplers. Prototypes for the 2-way and 3-way power dividers were manufactured on an LTCC multilayer substrate. Both measurement and full-wave simulation results are in excellent agreement and thus provide a proof of the concept.

An SIW-Based GaN Power Amplifier Module in LTCC

This article reports a solid-state power amplifier module in low-temperature cofired ceramic (LTCC) technology. For compactness and low loss, the package utilizes substrate-integrated waveguides (SIWs). To meet the thermal requirements, the amplifiers are mounted on a metallic plate that is integrated into the LTCC multilayer and transfers the heat to a spreader. Both RF and thermal measurement results for a package with two integrated 10-W gallium nitride (GaN) power amplifiers at the K-band are presented. They demonstrate the suitability of the module for highly integrated transmitters as needed for phased arrays or multiple-feed-per-beam satellite antennas.

Dimensioning and Realization of an LTCC Multilayer Capacitor for Energy Conversion

In this paper, we present the dimensioning as well as the thermal and electrostatic modelling of a multilayer capacitor low-temperature co-fired ceramic (LTCC) to insert it in a Buck converter. We also present the different stages of the realization of the LTCC capacitor. Our aims are volume and weight reduction, good frequency behaviour, low values of the series inductance and series resistance, and small ripples of the output voltage. The results obtained after the realization are satisfactory and encouraging, with a 92% reduction in volume and 99% in the surface area. To validate the correct operation of the capacitor, we used the PSIM simulation software to compare the voltage and current waveforms of the outputs of the Buck converter with a perfect capacitor and others with LTCC capacitor. COMSOL multiphysics simulation software allowed us to determine the operating temperature of the LTCC capacitor and to validate its electrostatic behaviour (distribution of electrical potential, of electrical field and electrical current density). The multilayer capacitor is manufactured in the LAPLACE laboratory at Paul Sabatier University.

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.

A Compact LTCC Decoupling-Network Based on Coupled-Resonator for Antenna Interference Suppression of Adjacent Frequency Bands

A low-temperature co-fired ceramic (LTCC) coupled resonator decoupling network (CRDN) with asymmetric input/output (I/O) couplings for suppressing interference between two adjacent frequency bands is proposed in this paper. Based on LTCC multilayer technology, a second-order CRDN module is realized by strongly coupled semi-lumped LC resonators in a very small volume of 3.2 mm $\times2.5$ mm $\times1.2$ mm. A wide range of mutual admittance and different self-admittances of the CRDN can be realized by adjusting the asymmetric I/O couplings. Thus, a satisfactory decoupling performance covering two contiguous bands, as well as good matching in each band, can be realized without additional matching networks. To prove the concept, two planar inverted-F antennas working in TD-LTE and Wi-Fi frequency bands, along with the corresponding decoupling network, are designed, fabricated, and tested. The measured results have demonstrated that more than 15-dB isolation improvement can be achieved within the two operating bands, showing the feasibility of this ”one-fit-all” integrated solution. More importantly, the design methodology and circuit topology presented in this paper are general and can be applied to practical multi-input multi-output system applications.

Thermal Management Study of LTCC PIN Photodiode Module

Multilayer low temperature co-fired ceramic (LTCC) is well known in usage as interconnect substrate, especially in high frequency application due to high electrical conductivity of the conductors and low loss of the LTCC dielectric. As substrate and packaging materials, there are many chips or devices placed on the multilayer LTCC board. In this paper, multilayer LTCC is implemented as the packaging at PIN photodiode (PD) module of the Radio over Fiber (RoF) system with the reason to increase thermal dissipation capacity of the PD module.

76–81 GHz LTCC antenna for an automotive miniature radar frontend

AbstractFor a fully 360° detection around a vehicle, novel automotive radar system concepts consist of up to eight radar sensors. The existing sensor-mounting areas, such as front grill or bumper corners would no longer be sufficient. Therefore, additional mounting positions such as B-pillars and side skirts have to be considered, where the radar can observe the side area of the vehicle. However, these new mounting positions usually offer significantly less space, than the established mounting areas. The solution is, to build separate miniature radar frontends that can be placed all over the vehicle and are connected to one central signal processing and power supply unit. Investigations for a miniature radar frontend have been done, based on RF360 low loss non-shrinkage low-temperature cofired ceramic (LTCC) substrate. For the automotive radar band (76–81 GHz), an array antenna has been simulated, manufactured, and the radiation pattern has been measured. A first sensor with a miniature radar frontend based on an LTCC multilayer has been designed and manufactured.

LTCC Filtering Rat-Race Coupler Based on Eight-Line Spatially-Symmetrical Coupled Structure

In this paper, a compact filtering rat-race coupler implemented in low-temperature co-fired ceramic (LTCC) technology is presented. In order to reduce the dimensions, the schematic and the coupling topology of a planar filtering rat-race coupler are first studied and then simplified to fit the 3-D multilayer LTCC structure. An eight-line spatially symmetrical coupled structure is, therefore, proposed to obtain the required coupling topology between resonators. Thus, the filtering rat-race coupler can be constructed only by using four resonators, which is only half that of the planar one. Consequently, the size could be reduced substantially. For validation, a design example centered at 3.5 GHz is simulated, fabricated, and measured. All the measured results are in good agreement with the full-wave simulation results. Besides, the size of the circuit is only $3.8 \times 4 \times 2.1$ mm3, which demonstrates that by employing the eight-line spatiallysymmetrical coupled structure, the proposed rat-race coupler obtains good performance and compact size.

Size-Reduced Planar and Nonplanar SIW Gysel Power Divider Based on Low Temperature Co-fired Ceramic Technology

Aiming at reducing the size of substrate integrated waveguide (SIW) Gysel power divider (PD), a SIW-based planar Gysel PD is redesigned based on low temperature co-fired ceramic (LTCC). In addition, another novel SIW-based nonplanar Gysel PD is first presented and implemented on multilayer LTCC, which can further reduce size over 83% when compared with planar Gysel PD. Both of the two SIW Gysel PDs are fabricated and measured, and the measured results show that within frequency range from 17 to 19 GHz, the planar Gysel PD has the performances of return losses 20 dB, and phase ripple about ±7.5°; while the nonplanar Gysel PD has the performances of return losses 10 dB, and phase ripple about ±7°.

Compact High-Isolation LTCC Diplexer Using Common Stub-Loaded Resonator With Controllable Frequencies and Bandwidths

In this paper, a low-temperature co-fired ceramic (LTCC) diplexer is presented with compact size and high isolation. By using the common stub-loaded resonator shared by two channel filters, combining and matching networks are eliminated and only three resonators are used to design the two second-order channel filters, resulting in simple structure and miniaturized size. A novel transmission path is utilized to not only realize the higher channel filter but also prevent the signal at the lower frequency band. And a specific coupling region is selected to simultaneously realize the coupling strength required by lower channel filter and a transmission zero at higher-band frequency. In this way, each channel filter can generate a transmission zero at the passband frequency of the other channel filter, resulting in high isolation. Moreover, the bandwidths and center frequencies of the two channel filters can be individually controlled due to the design flexibility of the multilayer LTCC structure. For demonstration, a diplexer operating at 3.5 and 5.5 GHz is fabricated. The core circuit has the compact size of 1.9 mm $\times1.7$ mm $\times2$ mm or $0.054~\lambda _{g} \times 0.048 \lambda _{g} \times 0.057~\lambda _{g}$ . Within the 3-dB passbands of the lower and higher channel filters, the measured isolation levels are better than 40 and 45 dB, respectively.

Multilayer LTCC structures based on glass-cordierite layers with different porosity

PurposeThe paper aims to report on fabrication procedure and present microstructure and dielectric behavior of multilayer porous low-temperature cofired ceramic (LTCC) structures based on glass-cordierite and glass-alumina.Design/methodology/approachThe LTCC structures were created as multi-layered composites with dense external layers and inner layers with intentionally introduced porosity. Two preparation methods were applied – subsequent casting of both kinds of slurries and conventional isostatic lamination of dried green tapes arranged in the designed order. Optical microscope observations were carried out to analyze the microstructure of green and fired multilayer structures and pore concentration. To evaluate the adhesion strength of the composite layers, pull test was performed. Dielectric behavior of the composites was studied in the frequency range 50 kHz-2 MHz.FindingsThe fabricated porous LTCC structures showed dielectric constant of 3-5.6. The lowest dielectric constant was attained for glass-cordierite composite made by the conventional tape casting/lamination/firing method from slurry with 50 per cent graphite content. The samples prepared using multiple casting were of worse quality than those fabricated in conventional process, contained irregular porosity, showed tendency for deformation and delamination and exhibited a higher dielectric constant.Originality/valueSearch for new low dielectric constant materials applicable in LTCC technology and new methods of their fabrication is an important task for development of modern microwave circuits.

94-GHz Compact 2-D Multibeam LTCC Antenna Based on Multifolded SIW Beam-Forming Network

This communication presents a compact 94-GHz 2-D multibeam antenna using the low-temperature co-fired ceramic (LTCC) technology. A good 2-D substrate integrated waveguide (SIW) beam-forming network (BFN) for eight beams is proposed, where four-phase shifters are properly introduced to increase the flexibility of the beams. Benefiting from multilayer LTCC, the BFN is compactly implemented in a completely symmetrical structure by using two multifolded SIW Butler matrixes with 50% reduction of the longitudinal size, and four couplers placed on different layers with interlaced signal routes to avoid overlaps or crossovers. Combined with a $2 \times 4$ SIW slot antenna array, the multibeam antenna can realize eight symmetric scanning beams on 2-D with stable gains for a wide coverage. For demonstration, the two single-port antennas with different pitch-angle beams are fabricated and measured, and good agreements with the expectations are observed. The differences of the beam orientations are less than 5°, while the measured peak gains of the beams are about 8.5 dBi.

Simulation of Heat Transfer by Cooling Channels in LTCC Substrate

The thermal resistance, flow analysis, pressure drop and distribution of coolant inside multilayer LTCC (Low Temperature Co-fired Ceramics) substrate are detailed investigated in this paper. For this reason four various structures of internal channels in the multilayer LTCC substrates were designed and simulated. The simulation 3D model consist of 6 LTCC of DuPont 951® layer with cooling microchannel in middle of substrate, power chips paced on top of LTCC and silver sintered joints under power chips. The impact of the structure of channels, volume flow and power loss of die was simulated, calculated and analyzed by using the simulation software Mentor Graphics FloEFDTM. The structure and size of channels have the significant impact on thermal resistance, pressure of coolant as well as the effectivity of cooling power components which can be placed on LTCC substrate. The thermal resistance was calculated from the temperature gradient among chip junction, the inlet fluid and the thermal load of chip. Optimizing and comparison of cooling channels structure inside LTCC substrates and analyzing the effect of volume flow for achieving the least thermal resistance of LTCC multilayer substrate is the main contribution of this paper.

Influence of various multilayer LTCC systems on dielectric properties’ stability in GHz frequency range

Purpose The purpose of this paper is to create multilayer substrate (composite) from various low temperature co-fired ceramic (LTCC) substrates by their mutual combinations and to analyse influence of these multilayer substrates on dielectric properties in GHz frequency range. Design/methodology/approach GreenTape 951, GreenTape 9K7 and Murata LFC were used to create compound multilayer substrates that include three layers: middle layer is from Murata LFC, and both upper and bottom layers are either from GreenTape 951 or GreenTape 9K7. Shrinkage in all x-, y- and z-axes of all substrates including multilayer substrates were analysed, and influence of different shrinkage on dielectric properties was examined by microstrip ring resonators applied on all mentioned of substrates. Findings The middle layer of Murata LFC has significant influence on shrinkage value of composites which has a good repeatability and minimalizes problems with design of multilayer LTCC devices. Impact of middle layer from Murata LFC on dielectric constant is not significant, but on the other hand Q factor (loss tangent) of these composites is increased according to inhomogeneity between single LTCC layers, especially at frequency around 6 GHz. Originality/value The novelty of this work lies in creating multilayers systems from different types of LTCC substrates to find combination with the most suitable physical and dielectric properties for various purposes in GHz range applications.

Subcritical crack growth in multilayer Low Temperature Co-fired Ceramics designed with surface compressive stresses

The strength of Low Temperature Co-fired Ceramics (LTCC) can be affected by the environmental conditions under which the material is loaded. In this work, the strength degradation associated with Subcritical Crack Growth (SCCG) mechanisms is investigated in several multilayer LTCC architectures designed with surface compressive residual stresses. The magnitude of the residual stresses was tailored combining two different LTCC materials. Biaxial strength measurements using the ball-on-three-balls method performed at room temperature in water (as reference environment) showed a clear increase in the characteristic strength with the compressive residual stress in the surface layer. The strength distribution in dependence of the surface stresses in the outer layer can be represented by a three-parameter Weibull distribution, thus providing a “threshold strength” (i.e. minimum strength) for the material. In addition, the use of compressive stresses in LTCCs introduces a threshold intensity factor for the SCCG behaviour, below which no environmental assisted cracking can occur.

Synthesis and Implementation of LTCC Bandpass Filter With Harmonic Suppression

In this paper, we utilize the coupling matrices to design a compact low-temperature cofired ceramic (LTCC) bandpass filter with wide stopband and high selectivity. One coupling matrix at the fundamental frequency is synthesized to obtain required passband responses. The other one at the third harmonic is manipulated to realize wide stopband. Two transmission zeros are appointed at both sides of the passband to enhance the skirt selectivity. They are generated by multiple cross-coupling paths, which are easy to realize in the multilayer LTCC structure. To reduce the circuit size, two coupled quarter-wavelength resonators are folded vertically and horizontally on different layers. An experimental filter is designed for verification. High skirt selectivity and wide stopband are observed in the measurement. Due to the LTCC techniques, the proposed circuit has a compact size of $2~\text {mm}\times 1.7~\text {mm}\times 2$ mm or $0.042\lambda _{g}\times 0.035\lambda _{g}\times 0.042\lambda _{g}$ . It is suitable for system-in-package applications.

Joining technologies for a temperature-stable integration of a LTCC-based pressure sensor

Abstract. Besides the well-known application as circuit boards and housings, multilayer low-temperature co-fired ceramics (LTCC) offer a flexible and temperature-stable platform for the development of complex sensor elements. Commercial LTCC qualities are usually available with a matching set of metallization pastes which allow the integration of various electrical functions. However, for the integration of ceramic sensor elements based on LTCC into standardized steel housings it is necessary to compensate the mismatching thermal expansion behaviour. Therefore balancing elements made of Kovar® (Fe–29 wt% Ni–17 wt% Co) and alumina ceramic (Al2O3) can be used. These components have to be joined hermetically to each other and to the LTCC sensors. In this study, brazing experiments were performed for combinations of Kovar–Al2O3 and Kovar–LTCC with Ag–Cu–Ti- and Ag–Cu–In–Ti-based commercial braze filler metals, Cusil-ABA® and Incusil®-ABA, respectively. For both active braze filler metals, optimized processing parameters were investigated to realize hermetic Kovar–Al2O3 and Kovar–LTCC joints.

Design and Analysis of LTCC-Integrated Planar Microstrip-to-Waveguide Transition at 300 GHz

A 300-GHz planar microstrip-to-waveguide transition in low-temperature co-fired ceramic (LTCC) is numerically and experimentally analyzed. A via fence and air holes are used to form a three-dimensional transition structure and a vertical hollow waveguide inside the multilayer LTCC substrate. The transition consists of a coplanar-waveguide-fed slot radiator backed by a short-wall of the waveguide and an open-circuited microstrip resonator. On the basis of the dual operation mechanism, the design guideline for the complex 3D structure is described using full wave analysis. The overall design is experimentally verified by a back-to-back transition which exhibits insertion loss of 4 dB at 300 GHz and 36-GHz bandwidth with better than 10-dB return loss. To evaluate the loss of a single transition, we carried out a loss component analysis by evaluating different lengths of microstrip line and hollow waveguide. The estimated loss for a single transition is 1 dB at 300 GHz. The planar transition without a metal back-short significantly reduces the size of terahertz packages and eliminates the need for additional components for hermetic sealing. The compact transition is easy to integrate in a low-cost LTCC package with an MMIC chip.

Cu<sub>3</sub>TeO<sub>6 </sub>Dielectric Thick Films: Processing by Electrophoretic Deposition and Electrical Characterization

Te-based compounds are promising dielectric candidates for Base-Metal Electrode Multilayer Ceramic Capacitors (BME-MLCCs) and Low-Temperature Co-fired Ceramics (LTCCs) applications due to their low sintering temperature and good dielectric properties. In spite of the possible compatibility with Cu electrodes for microelectronics, data on compounds of the CuO-TeO2 system are scarce. Recently, we have reported the phase formation process of Cu3TeO6 and the first dielectric data for Cu3TeO6 ceramics. Due to the interest for some applications in thick films, in this work Cu3TeO6 thick films were fabricated by electrophoretic deposition (EPD) on platinized silicon substrates under different processing conditions. The relation between processing and film’s quality was established. ~ 50 μm Cu3TeO6 thick films sintered at 860 oC for 5 h exhibit a permittivity of ~2 and dielectric loss of 0.01 at room temperature and the temperature coefficient of the dielectric permittivity is 9.5×103 ppm°C-1 at 1 MHz from 40 °C to 120 °C. It is expected that this dielectric performance, when compared with the one of Cu3TeO6 ceramic counterparts, improves if the density of the films is increased.

300-GHz Step-Profiled Corrugated Horn Antennas Integrated in LTCC

This paper presents 300-GHz step-profiled corrugated horn antennas, aiming at their integration in low-temperature co-fired ceramic (LTCC) packages. Using substrate integrated waveguide technology, the cavity inside the multi-layer LTCC substrate and a surrounding via fence are used to form a feeding hollow waveguide and horn structure. Owing to the vertical configuration, we were able to design the corrugations and stepped profile of horn antennas to approximate smooth metallic surface. To verify the design experimentally, the LTCC waveguides and horn antennas were fabricated with an LTCC multi-layer process. The LTCC waveguide exhibits insertion loss of 0.6 dB/mm, and the LTCC horn antenna exhibits 18-dBi peak gain and 100-GHz bandwidth with more than 10-dB return loss. The size of the horn antenna is only 5×5×2.8 mm 3 , which makes it easy to integrate it in LTCC transceiver modules.