High Temperature Cofired Research Articles

Scalable, Patternable Glass-Infiltrated Ceramic Radiative Coolers for Energy-Saving Architectural Applications.

A huge concern on global climate/energy crises has triggered intense development of radiative coolers (RCs), which are promising green-cooling technologies. The continuous efforts on RCs have fast-tracked notable energy-savings by minimizing solar absorption and maximizing thermal emission. Recently, in addition to spectral optimization, ceramic-based thermally insulative RCs are reported to improve thermoregulation by suppressing heat gain from the surroundings. However, a high temperature co-firing process of ceramic-based thick film inevitably results in a large mismatch of structural parameters between designed and fabricated components, thereby breaking spectral optimization. Here, this article proposes a scalable, non-shrinkable, patternable, and thermally insulative ceramic RC (SNPT-RC) using a roll-to-roll process, which can fill a vital niche in the field of radiative cooling. A stand-alone SNPT-RC exhibits excellent thermal insulation (≈0.251Wm-1 K-1 ) with flame-resistivity and high solar reflectance/long-wave emissivity (≈96% and 92%, respectively). Alternate stacks of intermediate porous alumina/borosilicate (Al2 O3 -BS) layers not only result in outstanding thermal and spectral characteristics, causing excellent sub-ambient cooling (i.e., 7.05 °C cooling), but also non-shrinkable feature. Moreover, a perforated SNPT-RC demonstrates its versatility as a breathable radiative cooling shade and as a semi-transparent window, making it a highly promising technology for practical deployment in energy-saving architecture.

Study on Tungsten Metallization and Interfacial Bonding of Silicon Nitride High-Temperature Co-Fired Ceramic Substrates

For the first time, Si3N4 HTCC has been prepared using W as the metal phase by high-temperature co-firing (1830 °C/600 KPa/2 h) as a potential substrate candidate in electronic applications. It was discovered that the addition of Si3N4 to the W paste has a significant impact on thermal expansion coefficient matching and dissolution wetting. As the Si3N4 content increased from 0 to 27.23 vol%, the adhesion strength of W increased continuously from 2.83 kgf/mm2 to 7.04 kgf/mm2. The interfacial bonding of the Si3N4 ceramic and the conduction layer was discussed. SEM analysis confirmed that the interface between Si3N4 and W exhibited an interlocking structure. TEM, HRTEM and XRD indicated the formation of W2C and W5Si3 due to the interface reactions of W with residual carbon and Si3N4, respectively, which contributed to the reactive wetting and good adhesion strength between the interface. Suitable amounts of Si3N4 powder and great interfacial bonding were the main reasons for the tough interfacial matching between the Si3N4 ceramic and the conduction layer.

Synergistic Au passivation and prolonged aging optimization enhance the long-term catalytic stability of porous YSZ/Pt electrodes

The catalytic activity of an oxygen-pumping electrode is very important to the performance of amperometric NOx (NO and NO2) sensors. To enhance the stability of electrochemical NOx sensors based on Pt electrodes, we fabricated sensitive electrodes of Pt-based materials doped with small and different Au contents on 8% mol Y2O3-stabilized ZrO2 (8YSZ) solid electrolyte substrates by screen printing and high-temperature co-firing. The effects of Au on the porous Pt electrode’s catalytic activity and long-term stability were investigated, and the results are as follows. First, the catalytic capacity of the Pt–Au alloy electrode decreases with increasing Au content due to the inhibition of the oxygen adsorption on Au, which decreases the amount of oxygen participating in the reaction at triple-phase boundaries (TPBs). Second, the catalytic ability of the alloy electrode decreases exponentially with aging time due to the reduction in the length of TPBs caused by the significant reduction in the number of holes in the electrode, and the oxidation of Pt. In addition, the conductivity decay rate of the electrode decreases with increasing Au doping. This indicates that Pt-based electrodes doped with varying Au contents, long-term, and high-temperature aging have notably regular effects on the catalytic activity of oxygen-pumping electrodes, for which we have developed a model of Au passivation and the synergistic effect of aging time on the activity of Pt-based oxygen-pumping electrodes.

Optimisation of Slurry Compositions for Improving the Mechanical Properties of Low Temperature Co-Fired Ceramic (LTCC) Tapes

In the era of miniaturization and hybridization, the quest for novel materials for multilayer packaging had been increased. The multilayer packaging includes High Temperature Co-Fired Ceramics (HTCC), LTCC and ULTCC. LTCC which is the mixture of ceramic and glass (which reduces the firing temperature of ceramics) has attracted many researchers due to its lower firing temperature(<900°C). Due to this lower sintering temperature, it can be cofired with the low resistance metals like Ag and Au which increases its value in multilayer packaging field. The standard package fabrication process uses LTCC in the form of tapes. Each layer can be processed separately for punching, via filling and Screen printing and then stacked, laminated and sintered to get a multilayer package. The green sheet of LTCC should have sufficient adhesion to carrier film as well as mechanical properties to withstand the fabrication processes that it undergoes. These properties are mainly affected by the organic compositions used in the slurry preparation. The tape casting slurry was prepared by blending the LTCC powder with solvents, dispersants and binders for a predefined time in ball mill. The as prepared slurry was casted on a Mylar sheet in a continuous tape caster for varied thickness. The present study aims at reporting the effect of plasticizers and binders on the adhesion and mechanical properties of the tape. The starting material which was the mixture of Cordierite and Anorthite based recrystallizable glass was prepared through solid-state method. The powder was then characterised for its phase purity, microstructure and elemental compositions using XRD, FESEM and EDAX. The green tapes were characterised for its thickness, uniformity, green and sintered density, surface defects such as pinholes and cracks, adhesion and tensile strength. The dielectric properties as well as thermal properties are also evaluated. The results are reported.

High temperature co-firing of 3D-printed Al[sbnd]ZnO/Al2O3 multi-material two-phase flow sensor

Sensors are crucial in the understanding of machines working under high temperatures and high-pressure conditions. Current devices utilize polymeric materials as electrical insulators which pose a challenge in the device's lifespan. Ceramics, on the other hand, is robust and able to withstand high temperature and pressure. For such applications, a co-fired ceramic device which can provide both electrical conductivity and insulation is beneficial and acts as a superior candidate for sensor devices. In this paper, we propose a novel fabrication technique of complex multi-ceramics structures via 3D printing. This fabrication methodology increases both the geometrical complexity and the device's shape precision. Structural ceramics (alumina) was employed as the electrical insulator whilst providing mechanical rigidity while a functional ceramic (alumina-doped zinc oxide) was employed as the electrically conductive material. The addition of sintering additives, tailoring the printing pastes' solid loadings and heat treatment profile resolves multi-materials printing challenges such as shrinkage disparity and densification matching. Through high-temperature co-firing of ceramics (HTCC) technology, dense high quality functional multi-ceramics structures are achieved. The proposed fabrication methodology paves the way for multi-ceramics sensors to be utilized in high temperature and pressure systems in the near future.

Free standing tapes of donor doped BaTiO3 for multilayer positive temperature coefficient thermistors

A disruptive method of fabricating free-standing tapes of La-doped (BaCaSrPb)TiO 3 thermistors is demonstrated. The greatest advantage is that the free-standing tapes do not require high temperature co-firing of electrodes or reduced environment cofiring — soft oxidation cycle to obtain thermal sensitivity. The approach thus solves the long-standing problem with the ceramic thermistor technology that eluded its compatibility with surface mount technology (SMT) and miniaturization. Stencil printing is employed that can fabricate up to 500 μm thick tapes in a single step, saving huge cost and processing steps for application requiring thicker films. The pastes suitable for freestanding tapes are reported. The method provides a novel route to integrate PTC elements into the chips of passive components and would lead to a massive reduction in cold resistivity when developed in multilayer laminated stacks.

Free standing tapes of donor doped BaTiO3 for multilayer positive temperature coefficient thermistors

A disruptive method of fabricating free-standing tapes of La-doped (BaCaSrPb)TiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> thermistors is demonstrated. The greatest advantage is that the free-standing tapes do not require high temperature co-firing of electrodes or reduced environment cofiring — soft oxidation cycle to obtain thermal sensitivity. The approach thus solves the long-standing problem with the ceramic thermistor technology that eluded its compatibility with surface mount technology (SMT) and miniaturization. Stencil printing is employed that can fabricate up to 500 μm thick tapes in a single step, saving huge cost and processing steps for application requiring thicker films. The pastes suitable for freestanding tapes are reported. The method provides a novel route to integrate PTC elements into the chips of passive components and would lead to a massive reduction in cold resistivity when developed in multilayer laminated stacks.

On-turbine multisensors based on Hybrid Ceramic Manufacturing Technology

Abstract The contribution evaluates the potential of piezoresistive multilayer ceramic sensory solutions using Low or High Temperature Cofired Ceramics (LTCC/HTCC) for on-turbine sensors. Relevant ceramic materials were characterized and evaluated with regard to applicability and reliability under application-like conditions. A multilayer ceramic sensory element was designed including a ceramic embedded pressure sensing membrane, a Pt100 temperature sensor and ceramic integrated wiring. Appropriate sealing methods to implement the ceramic into metal housings as well as electrical connection solutions were worked out, which allow for an operation under the increased temperatures (&amp;gt; 300°C) of the application. A system concept, including sensory element, signal conditioning electronics, mechanical and electrical interfaces is part of the investigation.

Self-heated HTCC-based ceramic disc for mixed potential sensors and for direct conversion sensors for automotive catalysts

Solid electrolyte gas sensors following the mixed potential sensing principle are usually operated at several hundred °C. They are often characterized using half-cell setups where one side of the sensor faces a reference gas atmosphere whereas the other side faces the gas mixture to be analyzed. Since two gas compartments are compared, a high temperature sealing is needed. Typically, such setups require indirect heating, and often, the manufacturing process is complicated and the dismantling of sensor and sealing is only possible by destroying it. To overcome these and other drawbacks of the half-cell setup, a self-heatable, stand-alone ceramic sensor device is developed in this work. We choose high temperature co-firing ceramics technology for the sensor design that bases on a self-heated yttria-stabilized zirconia disc that is hot enough for sensing in the central region and cold enough at the outer radius for contacting and plastic sealing. This work shows how problems that occurred due to the high thermal stress were overcome by employing finite element simulations. After developing and manufacturing the novel device, it is demonstrated that the sensor is capable to compare two gas mixtures electrochemically. For that purpose, the device was used to compare the gas composition up- and downstream of an oxidation catalyst. The sensor signal response correlates well with a theoretically derived dependence on the catalyst conversion.

Atmospheric plasma-sprayed BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) electrolyte membranes for intermediate-temperature solid oxide fuel cells

The high co-sintering temperature of BZCYYb electrolyte membranes supported by anode substrates usually causes a series of problems including undesirable electrolyte-anode reactions/diffusion and Ba-evaporation, posing a challenge for seeking alternative fabrication approaches. In this study, BZCYYb electrolyte membranes supported by anode substrates are fabricated by a large-scale and cost-effective atmospheric plasma spraying (APS) process. The 25µm thick BZCYYb membrane has negligible electrolyte-anode reactions/diffusion due to the APS process free of high-temperature co-firing. The Ba-evaporation problem is also resolved during APS process because of the adoption of large-grained BZCYYb feedstock powders. After 15 cycles of post-densification treatment by infiltrating, the plasma-sprayed BZCYYb membrane is dense enough for electrolyte application. The single cell based on dense plasma-sprayed BZCYYb electrolyte membrane shows a peak power density of 0.35Wcm−2 at 750°C using 3vol% humidified H2 as fuel and ambient air as oxidant.

A Three Electrode Mixed Potential Sensor for Gas Detection and Discrimination

Mixed potential solid state electrochemical sensors potentially serve as devices for detection of pollutants from industrial and automotive exhaust and can screen dangerous explosive chemicals in security sensitive areas. In these sensors the difference in catalytic activity between two electrode materials produces a voltage from the difference in the mixed potential that is established at steady state. By integrating multiple electrodes on a single substrate, each pair tuned to be sensitive to different gases, a device can be produced which is selectively sensitive to a variety of gases. The three-electrode sensors were fabricated by ESL ElectroScience with a high temperature co-firing technique on an insulator-YSZ-insulator substrate and Pt, La0.8Sr0.2CrO3 (LSCO), and Au0.5Pd0.5 electrodes were applied by screen printing. A porous YSZ layer over the electrodes serves as the electrolyte, and a length of Pt is printed on the back to serve as an integrated heater. The heating is applied by a control board which imposes a constant resistance, maintaining the temperature during the testing at various flow rates. The sensors were tested at 450-500oC in a 10% O2 atmosphere to different test gases which include NOx, CO, C3H8, (Figure 1) and mixtures of these gases. The Au/Pd+Pt pair is found to be most sensitive to NOx and CO, the LSCO+Pt pair is most sensitive to NOx and C3H8, and the Au/Pd+Pt pair is sensitive only to CO. Against 50-200 ppm backgrounds of NOx and C3H8, the introduction of 100 ppm CO to the gas stream yields a 30 mV response on the Au/Pd+Pt and Au/Pd+LSCO pairs, but produces less than 10 mV shift on the LSCO+Pt pair. Once sets of data consisting of voltage responses to blends of gases were collected, we successfully trained artificial neural networks to associate voltage responses with both binary gas mixture ratios and absolute concentrations of gases, as well as identify which mixtures of gases were present. Figure 1. Response of the three-electrode sensor at 450oC to different gases, where a preferential selectivity towards CO is seen in Au/Pd+Pt or Au/Pd+LSCO pairs and a selectivity towards C3H8 is seen in LSCO+Pt. Figure 1

High-performance solid oxide fuel cells based on a thin La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte membrane supported by a nickel-based anode of unique architecture

Solid oxide fuel cells (SOFCs) based on a thin La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte membrane supported by a nickel-based anode often suffers from undesirable reaction/diffusion between the Ni anode and the LSGM during high-temperature co-firing. In this study, a high performance intermediate-temperature SOFC is fabricated by depositing thin LSGM electrolyte membranes on a LSGM backbone of unique architecture coated with nano-sized Ni and Gd0.1Ce0.9O2−δ (GDC) particles via a combination of freeze-drying tape-casting, slurry drop-coating, and solution infiltration. The thickness of the dense LSGM electrolyte membranes is ∼30 μm while the undesirable reaction/diffusion between Ni and LSGM are effectively hindered because of the relatively low firing temperature, as confirmed by XRD analysis. Single cells show peak power densities of 1.61 W cm−2 at 700 °C and 0.52 W cm−2 at 600 °C using 3 vol% humidified H2 as fuel and ambient air as oxidant. The cell performance is very stable for 115 h at a constant current density of 0.303 A cm−2 at 600 °C.

Anode-supported Type SOFCs based on Novel Low Temperature Ceramic Coating Process

To prevent an interfacial reaction between the anode and the electrolyte layer during the conventional high-temperature co-firing process, an anode-supported type cell with a thin-film electrolyte was fabricated by low-temperature ceramic thick film coating process. Ni-GDC cermet composite was used as the anode material and YSZ was used as the electrolyte material. Open circuit voltage and maximum power density were found to strongly depend on the surface uniformity of the anode functional layer. By optimizing the microstructure of the anode functional layer, the open circuit voltage and maximum powder density of the cell increased to 1.11 V and 1.35 W/㎠, respectively, at 750℃. When a GDC barrier layer was applied between the YSZ electrolyte and the LSCF cathode, the cell showed good stability, with almost no degradation up to 100 h. Anode-supported type SOFCs with high performance and good stability were fabricated using a coating process.

Reduced-temperature firing of solid oxide fuel cells with zirconia/ceria bi-layer electrolytes

Solid oxide fuel cells (SOFCs) with bi-layer Zirconia/Ceria electrolytes have been studied extensively because of their great potential for producing high power density at reduced operating temperature, important for reducing cost and thereby allowing broader SOFC commercialization. The bi-layer electrolytes are designed to take advantage of the high oxygen ion conductivity of Ceria, the low electronic conductivity of Zirconia, and the low reactivity of Ceria with high-performance cathodes. However, zirconia/ceria processing has proven problematic due to interdiffusion during high temperature co-firing, or ceria layer porosity after two-step firing. Here we first show a new method for bi-layer co-firing at a reduced temperature of 1250 °C, ∼150 °C lower than the usual sintering temperature, achieved using Fe2O3 as a sintering aid. This novel process enables high power density SOFCs by producing: (1) low-resistance Y0.16Zr0.92O2−δ (YSZ)/Gd0.1Ce0.9O1.95 (GDC) electrolytes that also yield high open-circuit voltage, (2) dense GDC layers that prevent reactions between highly-active La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) cathode materials and YSZ, and (3) Ni–YSZ anodes with high electrochemical activity due to fine-scale microstructure with high TPB densities.

A 65-nm CMOS Fully Integrated Transceiver Module for 60-GHz Wireless HD Applications

This paper presents a fully integrated 60GHz transceiver module in a 65nm CMOS technology for wireless high-definition video streaming. The CMOS chip is compatible with the WirelessHD™ standard, covers the four channels and supports 16-QAM OFDM signals including the analog baseband. The ESD-protected die (9.3mm²) is flip-chipped atop a High Temperature Cofired Ceramic (HTCC) substrate, which receives also an external PA and the emission and reception glass-substrate antennas. The module occupies an area of only 13.5×8.5mm². It consumes 454mW in receiver mode and 1.357W in transmitter mode (357mW for the transmitter and 1W for the PA).

Novel Technology Options for Multilayer-Based Ceramic Microsystems

Ceramic multilayer technologies as LTCC (Low Temperature Cofired Ceramics) or HTCC (High Temperature Cofired Ceramics) are applied for the fabrication of highly integrated ceramic microelectronic packages. Furthermore ceramic multilayer technologies offer the possibility of the additional integration of 3-D-structures for multilayer-based microsystems. The paper presents a new machine for tape/ multilayer structuring combining micro punching tools and micro UV-laser ablation/ cutting. The application for the production of different multilayer based components is described (e.g. LTCC-based PEM fuel cell system, LTCC-based pressure sensors). Aerosol printing is a new technology e.g. for rapid prototyping for LTCC multilayer and 3-D-deposition of functional layers on LTCC. Advantages and limitations of the technology are discussed.

Short-period segmented-in-series solid oxide fuel cells on flattened tube supports

Segmented-in-series solid oxide fuel cells (SIS-SOFCs) were prepared on flattened-tube partially stabilized zirconia supports. The distinguishing characteristic of these cells was the short repeat period, 2.4 mm, and small active cell length, 1.3 mm, compared to ≈10 mm in previous SIS-SOFCs. The support tubes, formed by gelcasting, were bisque fired and then screen printing was used to sequentially deposit Ni-YSZ anodes, YSZ electrolytes, and Pt-YSZ composite interconnects. After high-temperature co-firing, LSM–YSZ and LSM cathode layers were screen printed and fired. Each flattened tube side had 12–16 individual cells. For testing, the open tube ends were sealed and humidified hydrogen flowed inside of the tubes; air was flowed over the outside of the tubes. Maximum total power at 800 °C was ≈8 W and maximum power density was ≈0.7 W cm −2, calculated using cell active area. Good stability was observed during a ≈650 h steady-state test. Excellent stability was also observed over ≈20 redox cycles.

00/02485 Characterization of ashes and deposits from high-temperature coal-straw co-firing

00/02485 Characterization of ashes and deposits from high-temperature coal-straw co-firing