Low Temperature Co-fired Ceramic Process Research Articles

Low-permittivity BaCuSi4O10-based dielectric Ceramics: An available solution to connect low temperature cofired ceramic technology and millimeter-wave communications

Low temperature cofired ceramic (LTCC) technology can serve for next-generation millimeter-wave electronic products to bring the advantages of integration, miniaturization and excellent high-frequency performance. However, challenges such as the performance of LTCC powders, quality of green tapes and Ag co-firing compatibility still need to be addressed for the application of LTCC technology. In this work, a systematic investigation from powder modification, LTCC process to filter design were carried out based on novel BaCuSi4O10-based dielectric ceramics. Multiple effects in terms of suitable sintering temperature (840 ℃ suit for Ag co-firing), low-permittivity (εr ∼ 5.7) and good thermal stability (temperature coefficient of resonant frequency ∼ − 27 ppm/℃, thermal expansion coefficient ∼3.9 ppm/℃) were achieved by introducing Li-B-Si glass and LiF composite additive. The origin of dielectric response of this LTCC system were discussed using the FIR reflectivity spectrum and THz-TDS. After optimizing the tape casting process for the LTCC powder, green tapes with uniform thickness, smooth surface and no cracking were obtained. Furthermore, the bandpass and lowpass filters exhibited a high level of filtering performance own to excellent dielectric properties and low surface roughness of the LTCC. Consequently, the BaCuSi4O10-based dielectric ceramic is an attractive candidate as LTCC technology expands into millimeter-wave communications.

A 39 GHz Dual-Channel Transceiver Chipset with an Advanced LTCC Package for 5G Multi-Beam MIMO Systems

A 39-GHz dual-channel CMOS transceiver chipset with an advanced LTCC packaging and the demonstration of a proposed dynamic multi-beam architecture based on the chipset for 5G MIMO applications. This article presents a 39 GHz transceiver front-end chipset for 5G multi-input multi-output (MIMO) applications. Each chip includes two variable-gain frequency-conversion channels and can support two simultaneous independent beams, and the chips also integrate a local-oscillator chain and digital module for multi-chip extension and gain-state control. To improve the radio-frequency performance, several circuit-level improvement techniques are proposed for the key building blocks in the front-end system. Furthermore, an advanced low-temperature co-fired ceramic process is developed to package the 39 GHz dual-channel transceiver chipset, and it achieves low packaging loss and high isolation between the two transmitting (TX)/receiving (RX) channels. Both the chip-level and system-in-package (SIP)-level measurements are conducted to demonstrate the performance of the transceiver chipset. The measurement characteristics show that the TX SIP provides 11 dB maximum gain and 10 dBm saturated output power, while the RX SIP achieves 52 dB maximum gain, 5.4 dB noise figure, and 7.2 dBm output 1 dB compression point. Single-channel communication link testing of the transceiver exhibits an error vector magnitude (EVM) of 3.72% and a spectral efficiency of 3.25 bit·s −1 ·Hz −1 for 64-quadrature amplitude modulation (QAM) modulation and an EVM of 3.76% and spectral efficiency of 3.9 bit·s −1 ·Hz −1 for 256-QAM modulation over a 1 m distance. Based on the chipset, a 39 GHz multi-beam prototype is also developed to perform the MIMO operation for 5G millimetre wave applications. The over-the-air communication link for one- and two-stream transmission indicates that the multi-beam prototype can cover a 5–150 m distance with comparable throughput.

A low-cost multilayer piezoelectric actuator for ultrasonic motor stator driving fabricated by a low-temperature co-fired ceramic process

Multilayer piezoelectric ceramics have wide application prospects in the fields of precision driving and intelligent sensing owing to their low driving voltages and large strains. However, high sintering temperatures and expensive noble metal electrodes limit their application as multilayer piezoelectric ceramic actuators (MLAs) in conventional devices. In this study, a modified piezoelectric ceramic powder and Ag inner electrode were used to prepare a low-cost MLA with a low sintering temperature of 900 °C. The MLA showed superior piezoelectric properties with d33 = 3015 pC/N and a large electric-field-induced strain of 0.13% at 22.2 kV/cm. Moreover, the stator of the ultrasonic motor composed of this MLA produced the ideal vibration mode, and the maximum rotation speed of the ultrasonic motor was 192 r/min under a 50 g load, which verifies the applicability of this component in practical minimised devices. These results demonstrate a strategy for fabricating low-cost and high-precision micro-actuators for precision driving.

Dual-Band Patch Antenna Matching Network Comprised of Separated Ground Layers and via Posts for Adjustable Return Current Path

This paper proposes a dual-band antenna impedance matching network concept that features identical radiation characteristics. The concept is exemplified for millimeter-wave mobile devices but can be scaled to lower and higher frequency spectrum. The method is deduced through an introduction of an additional matching network consisting of inductive distributed elements to formulate adjustable return current paths. This is realized using fragmented ground plane and a series of vias. No modification of the antenna radiating element is required. This new class of matching network enables independent adjustment of the resonance frequencies while maintaining nearly-identical radiation patterns at both frequencies. For experimental verifications, the proposed antenna impedance matching network is fabricated using a low-temperature co-fired ceramic process. The measurement of this single element exhibits dual-band operations at 28.0 GHz and 39.0 GHz, obtaining the realized gain of 5.15 dBi and 5.42 dBi, respectively. In addition, a 1×4 phased array antenna is devised and studied to validate beamforming performances at both frequencies. With the integration of the beamforming circuit, a reconfigurable beamforming is demonstrated at 28.0 GHz, in which the peak measured gain is 10.83 dBi. At the second resonance frequency (39.0 GHz), a passive feeding network is employed to evaluation its beam scanning abilities, and the main beam peak realized gain of 10.40 dBi is ascertained. The result can be extended to any other frequencies while maintaining near-identical far-field characteristics.

A Compact Cavity-Based Leaky-Wave Antenna in a Low Temperature Co-Fired Ceramic Process With Improved Performance

An approach for improving the gain of the leaky-wave antenna (LWA) is presented in this paper. Embedding cavities in the structure leads to gain improvement. To validate the proposed method, it was implemented on a half-mode substrate integrated waveguide (HMSIW) LWA. The proposed HMSIW LWA was realized on a low temperature co-fired ceramic (LTCC) structure to achieve a compact structure. The key novelty of the proposed antenna is the gain improvement by using embedded cavities without increasing the antenna size. Applying the novel design method results in a measured peak realized gain of 7.6 dBi. Tapering the aperture leads to about 6 dB reduction of sidelobe level (SLL) in the upper hemisphere as well. The impedance matching frequency bandwidth of the antenna ranges from 28.3 to 29 GHz that falls within the 5G mm-wave frequency bands. The length, width, and thickness of the antenna are 40 mm, 16 mm, and 1 mm, respectively. The compactness, medium gain, and low loss of the proposed antenna make it a suitable candidate for 5G wireless devices. A good agreement between the measured and simulated results is observed.

Ink-jet printed ring resonator with integrated Microfluidic components

PurposeThe main purpose of this study is to test the performance of the ink-jet printed microwave resonant circuits on Low temperature co-fired ceramics (LTCC) substrates combined with microfluidic channels for sensor applications. Normally, conductive patterns are deposited on an LTCC substrate by means of the screen-printing technique, but in this paper applicability of ink-jet printing in connection with LTCC materials is demonstrated.Design/methodology/approachA simple microfluidic LTCC sensor based on the microstrip ring resonator was designed. It was assumed the micro-channel, located under the ring, was filled with a mixture of DI water and ethanol, and the operating frequency of the resonator was tuned to 2.4 GHz. The substrate was fabricated by standard LTCC process, and the pattern of the microstrip ring resonator was deposited over the substrate by means of an ink-jet printer. Performance of the sensor was assessed with the use of various volumetric concentrations of DI water and ethanol. Actual changes in concentration were detected by means of microwave measurements.FindingsIt can be concluded that ink-jet printing is a feasible technique for fast fabrication of micro-strip circuits on LTCC substrates, including microfluidic components. Further research needs to be conducted to improve the reliability, accuracy and performance of this technique.Originality/valueThe literature shows the use of ink-jet printing for producing various conductive patterns in different applications. However, the idea to replace the screen-printing with the ink-jet printing on LTCC substrates in connection with microwave-microfluidic applications is not widely studied. Some questions concerning accuracy and reliability of this technique are still open.

Research on Structurally Integrated Phased Array for Wireless Communications

Structurally integrated antenna is a kind of highly integrated microwave device with a load-bearing function, and it is usually installed on the structural surface of the air, water and ground vehicles. This paper presents the design, fabrication and testing of a novel structurally integrated Ka-band active antenna for airborne 5G wireless communications. The proposed antenna is mainly composed of three parts: a package layer, a control and signal process layer and a RF layer. In the RF layer, the microstrip antenna array, tile transmitting (Tx) modules, micro-channel heat sinks and a stripline feeding network are highly integrated into a functional block with a thickness of 2.8 mm. Electromechanical co-design methods are developed to design the active antenna array with the superstrates, and two schemes for designing micro-channel heat sinks are evaluated to obtain a uniform temperature distribution. The RF layer is fabricated by using the low-temperature cofired ceramic process, and the three layers are assembled to form the full-size antenna prototype. The mechanical and electromagnetic experiments are carried out, and the results demonstrate the feasibility of the structurally integrated active antenna for airborne wireless communications.

Wide-Band and Low-Profile LTCC Conformal Antenna Array With Mixed Feeding Network

As we know, the thickness mainly affects the yield of low-temperature co-fired ceramics (LTCC) device. There is a high risk of cracking for the thick structure in manufacture process especially for the curved one. In this paper, double-layer artificial magnetic conductors (AMCs), mixed feeding network and built-in wide-band laminated waveguide (LWG) with rectangular waveguide (RWG) transition are specially analyzed and designed. These structures all have low-profile characteristics. Thus, they are suitable for conformal LTCC process. The double-layer AMCs are presented to enhance the bandwidth and the gain of a Ka-band patch element. The thin mixed network consisting of microstrip line (MSL) and LWG is used to replace the thick multistage LWG network. An improved LWG-RWG transition integrated in LWG layer is designed to possess wider bandwidth. At last, the low-profile conformal 16 × 16 antenna array is designed, manufactured and tested. The measured results demonstrate that the low-profile conformal 16 × 16 antenna array has a good and stable performance with an enhanced impendence bandwidth of 12.17% and a high gain up to 26.9dB.

Compact 60 GHz Phased-Array Antennas With Enhanced Radiation Properties in Flip-Chip BGA Packages

Compact phased-array antennas embedded in flip-chip ball grid array (BGA) packages are proposed to operate over the unlicensed 60 GHz frequency band. Radiation properties are enhanced by designing novel corrugated soft-surface structures and implementing them using the low-temperature co-fired ceramic process with no extra cost and fabrication complexity. This is achieved by adjusting via land diameters of periodic grounded vias in top four layers of the package, which in fact create perfect magnetic boundaries between the phased-array antenna elements to modify the electric near-field distributions and consequently improve far-field characteristics including gain, cross polarization, sidelobe level, and beam steering. Low-loss transitions from flip-chip IC to antenna elements are designed with less than 0.1 dB amplitude and 2° phase imbalance over 50–70 GHz. Prototypes with/without soft-surface structures are fabricated to work with flip-chip ICs with/without switches. A USB-interface adapter and a waveguide-interface module with a compact vertical power combiner are proposed for the first time to experimentally evaluate the phased-array antenna while connected to the flip-chip RF IC. Significant miniaturizations and improvements are achieved over the wide frequency range of 56–67 GHz, demonstrating up to 7 dB reduction in sidelobe level, up to 4 dB reduction in cross polarization, and up to 3 dB enhancement in gain at different directions.

Design, Preparation, and Performance of a Planar Ignitor Inserted With PyroMEMS Safe and Arm Device

A planar ignitor-based on low temperature co-fired ceramic (LTCC) and pyrotechnical micro electro mechanical system (PyroMEMS) technologies was designed and prepared in this paper. The planar ignitor is mainly composed of output charge layer, silicon safe and arm (Si-S&A) layer, and LTCC circuit base. Si/Pb3O4, C6H2(NO2)3OK/KClO4, and B/KNO3 were selected as ignition charge, gas charge, and transfer charge, respectively. The ignition circuit and main structure of the planar igniter were made by the LTCC process. Si-S&A was etched from monocrystalline silicon, which does not need environmental force to disarm. Preparation process of main components of planar ignitor that is suitable for mass production was introduced in detail. Simulation of PyroMEMS S&A actuation based on pendulum method was performed to save time for proof test. Finally, experimental verification on PyroMEMS S&A actuation and combustion propagation of B/KNO3 transfer charge were completed successfully. Results show that the idea of a planar ignitor inserted with PyroMEMS S&A device is feasible. [2018-0075]

Low Temperature Cofiring and Dielectric Properties of Ca-Doped Al2O3/K2O3–B2O3–SiO2 Composite Ceramics for LTCC Applications

Al2O3/K2O3–B2O3–SiO2 low temperature cofired ceramics (LTCC) dielectric materials doped with CaCO3 were prepared by using a solid-state reaction. The microstructure and dielectric properties of Al2O3/K–B–Si borosilicate, together with the effects of Ca doping, were investigated. A new material system candidate of Al2O3/KBSiO borosilicate doped by Ca was achieved after sintering at 880°C, which presents an optimized performance on dielectric properties with a permittivity εr < 8 and dielectric loss tan δ ≤ 0.002 and excellent stabilities across very broad frequency and temperature ranges. Most importantly, the initial results have also indicated that the new dielectric composite material is well compatible with the existing LTCC process, suggesting a considerable potential for practical LTCC applications.

Design, Fabrication, and Performance Characterization of LTCC-Based Capacitive Accelerometers.

In this paper, two versions of capacitive accelerometers based on low-temperature co-fired ceramic (LTCC) technology are developed, different with respect to the detection technique, as well as the mechanical structure. Fabrication of the key structure, a heavy proof mass with thin beams embedded in a large cavity, which is extremely difficult for the conventional LTCC process, is successfully completed by the optimized process. The LC resonant accelerometer, using coupling resonance frequency sensing which is first applied to LTCC accelerometer and may facilitate application in harsh environments, demonstrates a sensitivity of 375 KHz/g over the full scale range 1 g, with nonlinearity less than 6%, and the telemetry distance is 5 mm. The differential capacitive accelerometer adopting differential capacitive sensing presents a larger full scale range 10 g and lower nonlinearity less than 1%, and the sensitivity is 30.27 mV/g.

A Multilayer Power Inductor Fabricated by Cofirable Ceramic/Ferrite Materials With LTCC Technology

A cofired hetero-laminated low-temperature cofired ceramics (LTCC) power inductor device comprising cofirable NiCuZn ferrite body and Zn2SiO4 ceramic layers was designed, manufactured, and characterized. These produced LTCC power inductors were revealed to possess excellent characteristics including high inductance of $2.0~\mu \text{H}$ , small volume of 2 $\times1.2\times0.9$ mm3 (0805 packaging standard), low resistance of $0.20~\Omega $ , large current handling capability of 430 mA, low cost, and wide operating temperature range via a combination of characterization tools. Unlike the previously reported ceramic/ferrite hetero-laminates fabrication method, the process introduced in this paper involves no extra buffer layer or mechanical pressing sinter. Instead, a conventionally standard LTCC process was used for manufacturing these power inductors. To select the NiCuZn ferrite body with simultaneous high inductance and current handling capability for targeted power inductor design, the saturation magnetization and intrinsic coercivity of a variety of NiCuZn ferrite body prepared under different compositions, additives, and sintering conditions were carefully measured via vibrating sample magnetometer and under swept superpositioned dc magnetic field. Then, the power inductors with uniform sizes were mass produced using the selected NiCuZn body and Zn2SiO4 ceramic layers. The microstructure, magnetic element interdiffusion, interior circuit position, and inductance were detailed examined utilizing scanning electron microscopy, energy-dispersive X-ray spectroscopy, industrial computerized tomography scan, and RF impedance/material analyzer.

60-GHz LTCC Differential-Fed Patch Antenna Array With High Gain by Using Soft-Surface Structures

This paper presents a 60-GHz $4 \times 4$ differential -fed patch antenna array using low-temperature cofired ceramic (LTCC) process. Wideband patch with L-shaped feeding scheme is adopted as antenna element, while differential substrate integrated waveguide feeding network with low insertion loss is applied for the integration of antenna array. The differential-fed structure improves the symmetry of radiation patterns and reduces the cross-polarization level significantly. To further suppress the surface wave and improve the gain of the antenna array, one kind of soft surface structure is proposed. The equivalent circuit model of the soft surface is developed for calculating its dispersion diagram and analyzing stopband characteristics. The simulated results indicate that the antenna gain enhancement can be up to 2 dB because of the proposed soft surface. For demonstration, one prototype using LTCC process is fabricated and measured. The measured 10-dB impedance bandwidth of the antenna array is 11.7%. The measured antenna peak gain of 18.62 dBi at 61.5 GHz and symmetrical radiation patterns with a low cross polarization of −25 dB across the whole operating frequency are achieved.

An Efficient Gain Enhancement Approach for 60-GHz Antenna Using Fully Integrated Vertical Metallic Walls in LTCC

The gain of antenna array operating at 60 GHz using low temperature cofired ceramic (LTCC) technology is enhanced, by introducing a simple, low-profile, and low-loss structure. Part of the radiated waves in the antenna array’s $E$ -plane is in-phase reflected, by fully integrated vertical metallic walls. Consequently, an improved gain performance can be obtained. The substrate integrated waveguide slot antenna array is implemented for demonstrations. Those vertical metallic walls, created by cofabricated open-air cavities, are placed at either side along the $H$ -plane of slot radiators. Investigations were conducted on those key parameters of a single-slot antenna with two vertical metallic walls, in order to have a better understanding on the effect of the walls. Two prototypes, which are a $1 \times 8$ (1-D) and a $4 \times 8$ (2-D) waveguide slot antenna array, have been separately developed for verifications. The dimensions of the developed antenna arrays are determined based on a compromise between the performance and the fabrication restraint in the LTCC process. Both antenna arrays can efficiently transmit data within a 1000 MHz (59.5–60.5 GHz) bandwidth for some narrow band applications. When compared with conventional antenna arrays without metallic walls, the proposed approach can achieve gain enhancement of about 4.4 dB for the 1-D case and 2.5–3.1 dB for the 2-D case, across the impedance bandwidth.

New ferrimagnetic garnets for LTCC-technology circulators

Abstract Yttrium Iron Garnet based ferrites are used in non-reciprocal devices like microwave circulators and isolators. The low dielectric and magnetic losses of those materials provide the required properties. The main drawbacks of circulators are their size and cost, due to complex mechanical assembling of the different materials. In order to simplify this complex manufacturing process, a possible solution would be to adapt the different materials to a common LTCC (Low Temperature Co-fired Ceramics) process: the circulators would be produced with an additive multilayer process. We showed that cationic substitutions (bismuth and copper) enable a considerable decrease of the sintering temperature of garnets, from about 1450°C to down to 950°C. Due to bismuth cations, a high permittivity is achieved allowing the reduction of the circulator size. Our most recent results show that it is possible to decrease this temperature down to 880°C, thanks to vanadium substitutions. This significant decrease of the sintering temperature leads to a compatible material for co-firing with gold and in particular with silver (melting point of 1064°C and 962°C respectively). Different assemblies of tapes were studied: ferrite with silver or gold, ferrite with dielectric and ferrite with dielectric and metallization. Physical analyses are exposed (dilatometry, coefficient of thermal expansion…) and magnetic and dielectric properties are discussed (permittivity and saturation magnetization). Moreover the first results of circulators in LTCC-technology with gold and silver screen printing are presented (transmission, isolation and return loss) and the compatibility of the different elements is analyzed.

A Multilayer LTCC Solution for Integrating 5G Access Point Antenna Modules

An integrated solution for the development of multilayer antenna modules for fifth-generation (5G) communications, based on low temperature cofired ceramic (LTCC), is presented. The design exploits the 3-D integration capabilities of the LTCC process, enabling the realization of a full-corporate feed network (CFN) in vertical configuration. A novel implementation of the CFN employing dielectric-embedded parallel plate waveguides (PPWs) is proposed. The PPW lines are delimited by via-rows. As opposed to standard substrate-integrated waveguide feed networks, guided fields are orthogonal to the via-rows and propagate along the vertical axis of the structure. The CFN feeds four long slots, without any coupling structure, and provides broadband operation. The final prototype comprises 18 LTCC tapes, with a total thickness of 3.4 mm. The measured −10-dB impedance bandwidth spans from 51.2 to 66 GHz (>25.2%). The module generates a fixed broadside beam, but multibeam operation in $H$ -plane can be easily achieved. In the 50–66-GHz band, the peak gain is 14.25 dBi and the average first side-lobe level in $H$ -plane is −20.6 dB. The proposed technology and the design concept are suited for highly integrated millimeter-wave systems, such as access points in the future $V$ -band high data-rate wireless networks.

A fully integrated LTCC Wilkinson power divider/combiner using a parasitic compensated 100 OHM RF resistor for 60 GHz wireless applications

ABSTRACTThis letter shows a fully integrated Wilkinson power divider/combiner using low temperature co‐fired ceramic (LTCC) process. This power divider/combiner has a screen printed resistor. Therefore, this is helpful to reduce cost and to enhance productivity. Using short stubs and increased dc resistance for 100 Ohm resistor was proposed to compensate parasitic effects due to the large size of printed resistor in LTCC process. The measurement results reveal that the insertion loss is −1.07 dB (Back‐to‐Back: −2.15 dB) at 60 GHz. The measured return loss is better than −15dB in the whole band of interest (57–64 GHz). © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:720–722, 2016

Antenna-in-package system integrated with meander line antenna based on LTCC technology

We present an antenna-in-package system integrated with a meander line antenna based on low temperature co-fired ceramic (LTCC) technology. The proposed system employs a meander line patch antenna, a packaging layer, and a laminated multi-chip module (MCM) for integration of integrated circuit (IC) bare chips. A microstrip feed line is used to reduce the interaction between patch and package. To decrease electromagnetic coupling, a via hole structure is designed and analyzed. The meander line antenna achieved a bandwidth of 220 MHz with the center frequency at 2.4 GHz, a maximum gain of 2.2 dB, and a radiation efficiency about 90% over its operational frequency. The whole system, with a small size of 20.2 mm×6.1 mm×2.6 mm, can be easily realized by a standard LTCC process. This antenna-in-package system integrated with a meander line antenna was fabricated and the experimental results agreed with simulations well.

Integration of Silver Heat Spreaders in LTCC utilizing Thick Silver Tape in the Co-fire Process

The integration density in semiconductor devices is significantly increased in the last years. This trend is already described by Moore's law what forecasts a doubling of the integration density every two years. This evolution makes greater demands on the substrate technology which is used for the first level interconnect between the semiconductor and the device package. Higher pattern resolution is required to connect more functions on a smaller chip. Also the thermal performance of the substrate is a crucial issue. The increased integration density leads to an increased power density, what means that more heat has to dissipate on a smaller area. Thus, substrates with a high thermal conductivity (e. g. direct bonded copper (DBC)) are utilized which spread the heat over a large area. However, the reduced pattern resolution caused by thick metal layers is disadvantageous for this substrate technology. Alternatively, low temperature co-fired ceramic (LTCC) can be used. This multilayer technology provides a high pattern resolution in combination with a high integration grade. The poor thermal conductivity of LTCC (3 … 5 W*m−1*K−1) requires thermal vias made of silver paste which are placed between the power chip and the heat sink and reduce the thermal resistance of the substrate. The via-pitch and diameter is limited by the LTCC technology, what allows a maximum filling grade of approx. 20 to 25 %. Alternatively, an opening in the ceramic is created, to bond the chip directly to the heat sink. This leads to technological challenges like the CTE mismatch between the chip and the heat sink material. Expensive materials like copper molybdenum composites with matched CTE have to be used. In the presented investigation, a thick silver tape is used to form a thick silver heat spreader through the LTCC substrate. An opening is structured by laser cutting in the LTCC tape and filled with a laser cut silver tape. After lamination, the substrate is fired using a constraint sintering process. The bond strength of the silver to LTCC interface is approx. 5.6 MPa. The thermal resistance of the silver structure is measured by a thermal test chip (Delphi PST1, 2.5 mm × 2.5 mm) glued with a high thermal conducting epoxy to the silver structure. The chip contains a resistor and diodes to generate heat and to determine the junction temperature respectively. The backside of the test structure is temperature stabilized by a temperature controlled heat sink. The resulting thermal resistance is in the range of 1.1 K/W to 1.5 K/W depending on the length of silver structure (5 mm to 7 mm). Advantages of the presented heat spreader are the low thermal resistance and the good embedding capability in the co-fire LTCC process.